Polymer coating for medical devices

ABSTRACT

Coatings are provided in which surfaces may be activated by covalently bonding a silane derivative to the metal surface, covalently bonding a lactone polymer to the silane derivative by in situ ring opening polymerization, and depositing at least one layer of a polyester on the bonded lactone. Biologically active agents may be deposited with the polyester layers. Such coated surfaces may be useful in medical devices, in particular stents.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.11/605,634 filed Nov. 28, 2006, which is a Division of pending U.S.patent application Ser. No. 10/366,767, filed Feb. 14, 2003, whichclaims priority to U.S. Provisional Application No. 60/357,573 filedFeb. 15, 2002, the complete disclosures of which are hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a polymer coated metal surface in which atleast one polymer layer is covalently bonded to the activated metalsurface. The polymer coating may contain one or more biologically activeagents. The polymer coated metal can be used in an implantable medicaldevice such as a stent. The invention further relates to methods ofcoating metals surfaces and preparing medical devices.

2. Description of the Related Art

Many surgical interventions require the placement of a medical deviceinto the body. While necessary and beneficial for treating a variety ofmedical conditions, the placement of metal or polymeric devices in thebody can give rise to numerous complications. Some of thesecomplications include increased risk of infection, initiation of aforeign body response resulting in inflammation and fibrousencapsulation, and/or initiation of a wound healing response resultingin hyperplasia and/or restenosis. These and other possible complicationsmust be dealt with when introducing a metal or polymeric device into thebody.

One approach to reducing the potential harmful effects of such anintroduction has been to attempt to improve the biocompatibility of thedevice. While there are several methods available to improve thebiocompatibility of devices, one method which has met with limitedsuccess is to provide the device with the ability to deliverbiologically active agents to the vicinity of the implant. By so doing,some of the harmful effects that can be associated with the implantationof medical devices can be diminished. For example, antibiotics can bereleased from the device to minimize the possibility of infection, andanti-proliferative drugs can be released to inhibit hyperplasia. Anotherbenefit to the local release of biologically active agents is theavoidance of toxic concentrations of drugs which are sometimes necessarywhen given systemically to achieve therapeutic concentrations at thesite where they are needed.

Those skilled in the art of medical devices have been challenged to meetthe several stringent criteria for implantable medical devices. Some ofthese challenges are: 1) the requirement, in some instances, for longterm (days, weeks, or months) release of biologically active agents; 2)the need for a biocompatible, non-inflammatory surface on the device; 3)the need for significant durability, particularly with devices thatundergo flexion and/or expansion when being implanted or used in thebody; 4) concerns regarding processability, to enable the device to bemanufactured in an economically viable and reproducible manner; and 5)the requirement that the finished device be capable of being sterilizedusing conventional methods.

Several implantable medical devices capable of delivering medicinalagents have been described. Several patents are directed to devicesutilizing biodegradable or bioresorbable polymers as drug containing andreleasing coatings, including Tang et al, U.S. Pat. No. 4,916,193 andMacGregor, U.S. Pat. No. 4,994,071. Other patents are directed to theformation of a drug containing hydrogel on the surface of an implantablemedical device, these include Amiden et al, U.S. Pat. No. 5,221,698 andSahatijian, U.S. Pat. No. 5,304,121. Still other patents describemethods for preparing coated intravascular stents via application ofpolymer solutions containing dispersed therapeutic material to the stentsurface followed by evaporation of the solvent. This method is describedin Berg et al, U.S. Pat. No. 5,464,650.

A number of approaches have been used to try to overcome the challengeslisted above. The below are examples of these approaches.

McPherson, et. al., U.S. Pat. No. 6,013,855, describes methods forgrafting hydrophilic polymers onto metal surfaces. This method includedexposing the device surface to a silane coupling agent and causing theagent to be covalently bound to the device surface. The bonded silanelayer was then exposed to a hydrophilic polymer such that thehydrophilic polymer became covalently bound to the silane layer.

Pinchuck, U.S. Pat. No. 5,053,048, describes curing a silane compound orcompounds onto a surface to form a hydrophilic matrix. Anantithrombogenic agent was then coupled to the amine group on theaminosilane three-dimensional matrix to provide a thromboresistantcoating to the surface.

Lee, et. al., U.S. Pat. No. 6,335,340, describes methods for coatingoxide surfaces and coatings that rendered such surfaces hydrophilic. Afunctional group (Z) such as SiCl₃ was associated with the surface. Atether of a hydrophobic covalent attachment, typically of approximately5 to 20 bonds in length, was formed with Z. A biopolymer-resistantdomain was then adhered to the tether to form the hydrophilic surface.

Hostettler, et. al., U.S. Pat. No. 6,265,016, describes chemicallytreating metal surfaces to affix amine-containing groups. A “tie coat”of a hydrophilic polyurethane was then covalently attached to the aminegroups to form a slippery, hydrophilic polyurethane hydrogel.

Kamath, et. al., U.S. Pat. No. 6,335,029, describes applying at leastone composite layer of a biologically active agent and a polymer to abase material by physical or covalent methods. At least one barrierlayer was positioned over and applied to the composite layer by a lowenergy plasma polymerization process.

Shah, et. al., U.S. Pat. No. 6,248,127, describes coatings for medicaldevices in which a silane coating is adhered on the surface of thesubstrate and a film containing a heparin-biopolymer complex is createdon the surface by covalent linkages.

However, there remain significant problems to overcome in order toprovide a durable implantable medical device capable of delivering atherapeutically effective amount of a biologically active agent for anextended period of time. This is particularly true when the coatingcomposition must be kept on the device in the course of flexion and/orexpansion of the device during implantation or use. It is desirable tohave a facile and easily processable method of controlling the rate ofbiologically active agent release from the surface of the device.

Although a variety of polymers have previously been described for use asdrug release coatings, only a small number possess the physicalcharacteristics that would render them useful for implantable medicaldevices which undergo flexion and/or expansion upon implantation. Manypolymers which demonstrate good drug release characteristics, when usedalone as drug delivery vehicles, provide coatings that are too brittleto be used on devices which undergo flexion and/or expansion. Otherpolymers can provide an inflammatory response when implanted. These orother polymers demonstrate good drug release characteristics for onedrug but very poor characteristics for another.

In many respects, the success of a polymer coating depends on the natureof the contact between at least the polymer layer adjacent to the metalsurface and the underlying metal surface. In particular, if the polymercracks or peels away from the metal surface, the polymer and anybiologically active agent contained therein may decrease in performance.If the polymer layer is designed to contain a biologically active agentto be released, the resulting polymer/biologically active agentcomposite may be prone to dilation, swelling, degradation, and/or volumechanges because of interactions of the incorporated compound withaqueous environments of the body. Also, following the penetration ofwater into the polymer layer, dissolution of the compound and itssubsequent release, may change the structure and porosity of thecomposite. In addition, due to penetration of water following drugdissolution, the polymer layer could be exposed to a mechanical stressdue to osmotic forces. These effects may result in detachment of thepolymer layer and its peeling from the metal surface. Further, thechanges in the geometry of the polymer layer and the available surfacearea are potential sources of unpredictability of the release rate forthe incorporated compounds. Due to a combination of these factors, theperformance of the system decreases.

Accordingly, there is a persistent need for an improved polymer coatingof metallic implants that provides a stable, biocompatible andlow-profile polymer coating that, at the same time, provides a long-termrelease of biologically active agents for periods extending to weeks ormonths. Thus, there is a need for a method for securing the highlyreproducible deposition of the polymer coating layer on the articlesurface. In many instances the polymer layer has to be thin enough sothat it does not restrict the flexibility and adaptation of the metaldevice. Also, the polymer layer must resist damage due to devicehandling or deformation.

SUMMARY OF THE INVENTION

The invention provides for a coating for a metal surface with ametal-activating layer of polymerized silane derivatives covalentlybound to the metal surface. A binding layer of one or more lactonepolymers is covalently bonded to the polymerized silane derivative. Thesurface may further include a container layer of one or more sublayersof a polymer adhered to the binding layer.

In one embodiment of the invention, the composition of the binding layeror the container layer, or both, includes one or more biologicallyactive agents. The biologically active agent(s) is about 0 to about 60percent by weight of the binding or container layers. The biologicallyactive agent is released from the composition in an aqueous environment.

In another embodiment of the invention, the metal-activating layer is asiloxane polymer having one or both of hydroxy- or amino-groups on thesiloxane. The siloxane polymer is acylated by the polyester of thebinding layer.

The binding layer and the container layers have at least one layer ofone or more lactone polymers.

In the binding layer, the lactone polymer may be a lactone homopolymersuch as polyglycolide, poly(L-lactide), poly(D-lactide),poly(E-caprolactone), poly(p-dioxanone), poly(dioxepanone), or a lactonecopolymer such as poly(L-lactide-co-D-Lactide),poly(L-lactide-co-glycolide), poly(D-lactide-co-glycolide),poly(D,L-lactide-co-glycolide), poly(lactide-co-caprolactone),poly(lactide-co-dioxanone), poly(D,L-lactide), orpoly(lactide-co-dioxepanone).

In the container layer, the polyester polymer may be either a lactonehomopolymer, a statistical copolymer, or a block copolymer with at leastone polylactone block, while the other block or blocks of the copolymermay be a polyether, a poly(amino acid), a poly(acrylate), apoly(methacrylate), or polybutadiene. In a preferred embodiment of theinvention, the polymer of the container layer has a molecular weight of10³ to 10⁶.

In various preferred embodiments, the binding layer is a polylactide andthe container layer is one or more polymers such as poly(L-lactide),poly(glycolide), poly(lactide-co-glycolide) orpoly(L-lactide-co-D-lactide), and the mole fraction of L-lactidestructural units is in the range of either 0.7 to 1.0 or 0 to 0.3. Thebiologically active agent is about 0.5 to 60 percent of the total massof polymer of the container layer.

In other preferred embodiments of the invention, the binding layer is apolylactide and the container layer is a polymer selected ofpoly(D,L-lactide) or poly(L-lactide-co-D-lactide) and the mole fractionof L-lactide structural units is in the range of 0.3 to 0.7. Thebiologically active agent is 0.5 to 60 percent of the total mass ofcontainer layer.

In still another embodiment of the invention, the container layer hastwo or more sublayers of the same or different polymers. Theconcentration of the biologically active agent(s) in an inner containersublayer may be different than the concentration of the biologicallyactive agent(s) in an outer container sublayer.

In another preferred embodiment of the invention, the composition of theinner container sublayer is a semicrystalline polymer, or asemicrystalline mixture of polymers, and the outer container sublayercomprises at least one amorphous polymer. The polymer of an innercontainer sublayer may be a hydrophobic polymer which is either alactone homopolymer, a statistical lactone copolymer, a lactone blockcopolymer, and the polymer of an outer container sublayer is anamphiphilic copolymer of at least one of a statistical copolymer and ablock copolymer of lactones and ethylene oxide.

Yet another embodiment of the invention includes a method of coating ametal surface. The method includes reacting the metal surface with asilane-based activating reagent to form a metal surface having anactivated layer, polymerizing at least one lactone via ring openingpolymerization in the presence of the activating layer to form a metalsurface having a binding layer, and depositing at least one solventsolution comprising a polymer on the binding layer and evaporating thesolvent to form at least one container layer adhered to the bindinglayer. The silane-based activating reagent is a silane derivative ofgeneral formula (R²)₃—SiR¹ wherein R¹ is independently selected fromsubstituted alkyl, substituted alkenyl, substituted alkynyl, substitutedaralkyl, substituted heteroaryl, and substituted alkoxy, with theproviso that R¹ contains a hydroxy or amino group, or a functional groupthat can be transformed to a radical that contains a hydroxy or aminogroup; wherein R² is independently selected from halo, optionallysubstituted alkoxy, optionally substituted aryloxy, optionallysubstituted silyloxy, or optionally substituted alkyl, with the provisothat all three R² substituents are not simultaneously substituted alkyl.

In a preferred embodiment, the silane-based activating reagent is anorgano-trialkoxysilane derivative of a general formula R′—Si—(OR)₃ whereR is a C₁₋₄ alkyl group, and R′ is a hydroxyalkyl, aminoalkyl, or afunctional group that can be transformed to hydroxyalkyl or aminoalkylthrough a modification reaction.

In another preferred embodiment the silane-based activating agent isapplied in a solution or in a vapor phase to form a metal activatinglayer bound to the metal surface. Formation of a binding layer bylactone polymerization includes immersing an activated metal surface ina lactone solution, or a lactone melt at a temperature sufficient tokeep the lactone in the molten state, while both environments alsocontain a polymerization catalyst, for a time sufficient to allow thein-situ ring opening polymerization of the lactone on the activatedlayer to form the binding layer. Formation of a container layer includesthe deposition of a solvent solution containing the polymer onto thebinding layer by bringing a metal surface having the activation layerand binding layer into contact with a polymer solution by dipping thesurface into the solvent solution or spraying, casting, pouring orspreading the solution onto the surface, and evaporating the excesssolvent. The solvent solution may contain one or more biologicallyactive compounds. In certain embodiments, the solvent is an aproticsolvent such as an ether, ketone, aromatic hydrocarbon and a mixture ofthese solvents. The catalyst may be a low-toxicity catalyst suitable forring-opening polymerization of lactones by a coordination-insertionmechanism. The catalyst includes tin(II), zinc, calcium carboxylates,iron carboxylates, and alkyl aluminum compounds.

In still another embodiment of the invention, the polymer of thecontainer layer is compatible with the polymer of the binding layer. Thecontainer layer may be formed by deposition of one or more successivesublayers of polymer over the binding layer. Each sublayer of polymermay have the same composition as the previous container sublayer or eachsublayer may vary in polymer composition. Each of these successivelayers of polymer may contain one or more biologically active agents.

In yet another embodiment, the invention provides for a medical devicehaving a metal surface with a metal-activating layer of polymerizedsilane derivatives covalently bonded to the metal surface, a bindinglayer of a polylactone covalently bonded to the polymerized silanederivatives, and a container layer of a polymer adhered to the bindinglayer, where the container layer has a biologically active agent(s)releaseably associated with the polymer. The biologically activeagent(s) may be about 0.5 to 60% by weight of the container layer.

In a further preferred embodiment, the medical device is, for example, astent, vascular graft tubing, a blood oxygenator, an intravascularballoon, a catheter, an implantable pulse generator, an electrode, anelectrical lead, sutures, a soft or hard tissue prosthesis, or anartificial organ. The container layer and the binding layer include oneor more sublayers of one or more polylactone polymers. The polymers maybe a lactone co-polymer that may include block copolymers of least onepolylactone block.

In another preferred embodiment, the container layer has two or moresublayers of the same or different polymers. The concentration of thebiologically active agent(s) in an inner container sublayer may bedifferent than the concentration of the biologically active agent in anouter container sublayer.

In another preferred embodiment, at least one barrier or skin layer isprovided on top of the container layer. The composition of the barrieror skin layer may be different from the composition of the outermostcontainer layer sublayer,

DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic representation of the coated metal surface of theinvention.

FIG. 2 is a schematic representation of the mechanism and structureinvolved in the reactive adsorption of alkoxysilane activating reagenton surfaces containing metal oxide groups.

FIG. 3 is a graph showing the release of a biologically active agentfrom a coated metal surface of the present invention. The cumulativeamount (in mg) of CVT313 released from PDLLA films to PBS plottedagainst time (days) for different initial concentrations (w/w) of CVT313in the film (n=3); o-series G (initial conc 10.3%); Δ-series H (initialconc 18.9%); +-series J (initial conc 25.1%).

FIG. 4 is a graph showing the release of a biologically active agentfrom a coated metal surface of the present invention. Comparison of therelease from plates of series N (open points) and P (filled points)showing the effect of PDLLA skin layer on the release of CVT313 from thesame container matrix (PLLA) (n=4).

FIG. 5 is a graph showing the controlled release of dexamethasone fromPDLLA coated stainless steel plates for PDLLA/dexamethasone compositionwith different dexamethasone loading: series A (n=3), 19/6% w/w (filledpoints); series B (n=3) 12.8% w/w (open points).

FIG. 6 is graph showing the release rate profile of CVT313 from coatedcoronary stents of the present invention. The symbols show the measuredvalues for individual stents (n=3). The line represents the averagevalues.

FIG. 7 is a graph showing the release rate for the same data shown inFIG. 6 on a square-root of time scale. The cumulative amount of releasedCVT313 from coated coronary stents in % of total loading plotted on asquare-root-of-time scale. The symbols show the measured values forindividual stents (n=3). The line represents the linear fit. The lineardependence of the released amount on the square-root-of-time indicatesthe compliance with the diffusion controlled mechanism of release,typical for the monolithic matrix devices. Higuchi, T., Rate of releaseof medicaments from ointment bases containing drugs in suspensions. J.Pharm. Sci., 50: 874-875 (1961); Higuchi, T., Mechanism ofsustained-action medication, theoretical analysis of rate of release ofsolid drugs dispersed in solid matrices. J. Pharm. Sci., 52: 1145-1149(1963).

FIG. 8 is a graph showing the release rate profile for CVT313 fromcoated metal surfaces of the present invention. The fraction of CVT313released over 10 days period from the series of coating films formed bypolylactide compositions with different ratio of L-lactide and D-lactidestructural units. Series Q (filled circles): PLLA (L-LA/D-LA=1.00);series R (open circles): PLLA/PDLLA 3:1 blend (L-LA/D-LA=0.88); series S(triangles): PLLA/PDLLA 1:1 blend (L-LA/D-LA=0.75); series T (opensquares): P-LL-co-DL (L-LA/D-LA=0.75); and series U (filled squares):PDLLA (L-LA/D-LA=0.5).

DETAILED DESCRIPTION OF THE INVENTION

We recently found the requirements for biologically activecompound-releasing polymer coatings for implantable medical devices canbe met by using polyester-based polymer coatings. The polymer coatingcan improve the performance of the device by providing a biocompatibleinterface between the metal surface and the surrounding tissue, whilethe biological response of the organism, namely the local response ofthe surrounding tissue, can be modulated by sustained release of asuitable biologically active agent(s). We found that a low-profilepolymer layer, that does not significantly affect mechanical propertiesof the device and that provides for a long-lasting matrix reservoir fora biologically active agent(s) to be released in a controlled manner,can be produced by a successive deposition of chemically compatiblepolymers on the metal surface of the implantable device. First, anactivating silane derivative interfacing the metal surface is covalentlybound to the metal surface to activate the surface and provide forsuitable functional groups. Second, a polymer (binding) layer iscovalently bound to the activating layer. The covalent binding of thefirst polymer binding layer provides for good adhesion of any subsequentpolymer layers to the surface of the device. This allows for a thin,durable and contiguous film having a release performance which can beadjusted in a reproducible manner. This method is applicable for usewith biocompatible, medically applicable polymers, thus making themethod suitable for coating medical devices.

Before proceeding further with a description of the specific embodimentsof the present invention, a number of terms will be defined.

The term “alkyl” refers to a monoradical branched or unbranchedsaturated hydrocarbon chain having from 1 to 20 carbon atoms. This termis exemplified by groups such as methyl, ethyl, n-propyl, iso-propyl,n-butyl, iso-butyl, t-butyl, n-pentyl, 2-methylbutyl, n-hexyl, n-decyl,tetradecyl, and the like.

The term “substituted alkyl” refers to (1) an alkyl group as definedabove, having from 1 to 5 substituents, preferably 1 to 3 substituents,selected from the group consisting of alkenyl, alkynyl, alkoxy,cycloalkyl, cycloalkenyl, acyl, acylamino, acyloxy, amino,aminocarbonyl, alkoxycarbonylamino, azido, cyano, halogen, hydroxy,keto, thiocarbonyl, carboxy, carboxyalkyl, arylthio, heteroarylthio,heterocyclylthio, thiol, alkylthio, aryl, aryloxy, heteroaryl,aminosulfonyl, aminocarbonylamino, aminothiocarbonylamino,aminothiocarbonylamio, heteroaryloxy, heterocyclyl, heterocyclooxy,hydroxyamino, alkoxyamino, nitro, —SO-alkyl, —SO-aryl, —SO-heteroaryl,—SO₂-alkyl, SO₂-aryl and —SO₂-heteroaryl. Unless otherwise constrainedby the definition, all substituents may be optionally furthersubstituted by alkyl, alkoxy, halogen, CF₃, amino, substituted amino,cyano, or —S(O)_(n)R, in which R is alkyl, aryl, or heteroaryl and n is0, 1 or 2; (2) an alkyl group as defined above that is interrupted by1-5 atoms or groups independently chosen from oxygen, sulfur and—NR_(a)—, where R_(a) is chosen from hydrogen, alkyl, cycloalkyl,alkenyl, cycloalkenyl, alkynyl, aryl, heteroaryl and heterocyclyl. Allsubstituents may be optionally further substituted by alkyl, alkoxy,halogen, CF₃, amino, substituted amino, cyano, or —S(O)_(n)R, in which Ris alkyl, aryl, or heteroaryl and n is 0, 1 or 2; or (3) an alkyl groupas defined above that has both from 1 to 5 substituents as defined aboveand is also interrupted by 1 to 5 atoms or groups as defined above.

The term “alkylene” refers to a diradical of a branched or unbranchedsaturated hydrocarbon chain, preferably having from 1 to 20 carbonatoms, preferably 1 to 10 carbon atoms, more preferably 1 to 6 carbonatoms. This term is exemplified by groups such as methylene (—CH2-),ethylene (—CH2CH2-), the propylene isomers (e.g., —CH2CH2CH2- and—CH(CH₃)CH2-) and the like.

The term “substituted alkylene” refers to (1) an alkylene group asdefined above having from 1 to 5 substituents selected from the groupconsisting of alkyl, alkenyl, alkynyl, alkoxy, cycloalkyl, cycloalkenyl,acyl, acylamino, acyloxy, amino, aminocarbonyl, alkoxycarbonylamino,azido, cyano, halogen, hydroxy, keto, thiocarbonyl, carboxy,carboxyalkyl, arylthio, heteroarylthio, heterocyclylthio, thiol,alkylthio, aryl, aryloxy, heteroaryl, aminosulfonyl, aminocarbonylamino,aminothiocarbonylamino, heteroaryloxy, heterocyclyl, heterocyclooxy,hydroxyamino, alkoxyamino, nitro, —SO-alkyl, —SO-aryl, —SO-heteroaryl,—SO₂-alkyl, SO₂-aryl and —SO₂-heteroaryl. Unless otherwise constrainedby the definition, all substituents may be optionally furthersubstituted by alkyl, alkoxy, halogen, CF₃, amino, substituted amino,cyano, or —S(O)_(n)R, in which R is alkyl, aryl, or heteroaryl and n is0, 1 or 2; (2) an alkylene group as defined above that is interrupted by1 to 5 atoms or groups independently chosen from oxygen, sulfur andNR_(a)—, where R_(a) is chosen from hydrogen, optionally substitutedalkyl, cycloalkyl, cycloalkenyl, aryl, heteroaryl and heterocycyl, orgroups selected from carbonyl, carboxyester, carboxyamide and sulfonyl;or (3) an alkylene group as defined above that has both from 1 to 5substituents as defined above and is also interrupted by 1 to 20 atomsas defined above. Examples of substituted alkylenes includechloromethylene (—CH(Cl)—), aminoethylene (—CH(NH₂)CH₂—),methylaminoethylene (—CH(NHMe)CH₂—), 2-carboxypropylene isomers(—CH₂CH(CO₂H)CH₂—), ethoxyethyl (—CH₂CH₂O—CH₂CH₂—),ethylmethylaminoethyl (—CH₂CH₂N(CH₃)CH₂CH₂—),1-ethoxy-2-(2-ethoxy-ethoxy)ethane (—CH₂CH₂O—CH₂CH₂—OCH₂CH₂—OCH₂CH₂—),and the like.

The term “aralkyl” refers to an aryl group covalently linked to analkylene group, where aryl and alkylene are defined herein. “Optionallysubstituted aralkyl” refers to an optionally substituted aryl groupcovalently linked to an optionally substituted alkylene group. Sucharalkyl groups are exemplified by benzyl, phenylethyl,3-(4-methoxyphenyl)propyl, and the like.

The term “alkoxy” refers to the group R—O—, where R is optionallysubstituted alkyl or optionally substituted cycloalkyl, or R is a group—Y-Z, in which Y is optionally substituted alkylene and Z is optionallysubstituted alkenyl, optionally substituted alkynyl, or optionallysubstituted cycloalkenyl, where alkyl, alkenyl, alkynyl, cycloalkyl andcycloalkenyl are as defined herein. Preferred alkoxy groups areoptionally substituted alkyl-O— and include, by way of example, methoxy,ethoxy, n-propoxy, iso-propoxy, n-butoxy, tert-butoxy, sec-butoxy,n-pentoxy, n-hexyloxy, 1,2-dimethylbutoxy, trifluoromethoxy, and thelike.

The term “alkenyl” refers to a monoradical of a branched or unbranchedunsaturated hydrocarbon group preferably having from 2 to 20 carbonatoms, more preferably 2 to 10 carbon atoms and even more preferably 2to 6 carbon atoms and having 1 to 6, preferably 1, double bond (vinyl).Preferred alkenyl groups include ethenyl or vinyl (—CH═CH₂), 1-propyleneor allyl (—CH₂CH═CH₂), isopropylene (—C(CH₃)═CH₂),bicyclo[2.2.1]heptene, and the like. In the event that alkenyl isattached to nitrogen, the double bond cannot be alpha to the nitrogen.

The term “substituted alkenyl” refers to an alkenyl group as definedabove having from 1 to 5 substituents, and preferably 1 to 3substituents, selected from the group consisting of alkyl, alkenyl,alkynyl, alkoxy, cycloalkyl, cycloalkenyl, acyl, acylamino, acyloxy,amino, aminocarbonyl, alkoxycarbonylamino, azido, cyano, halogen,hydroxy, keto, thiocarbonyl, carboxy, carboxyalkyl, arylthio,heteroarylthio, heterocyclylthio, thiol, alkylthio, aryl, aryloxy,heteroaryl, aminosulfonyl, aminocarbonylamino, aminothiocarbonylamino,heteroaryloxy, heterocyclyl, heterocyclooxy, hydroxyamino, alkoxyamino,nitro, —SO-alkyl, —SO-aryl, —SO-heteroaryl, —SO₂-alkyl, SO₂-aryl and—SO₂-heteroaryl. All substituents may be optionally further substitutedby alkyl, alkoxy, halogen, CF₃, amino, substituted amino, cyano, or—S(O)_(n)R, in which R is alkyl, aryl, or heteroaryl and n is 0, 1 or 2.

The term “alkynyl” refers to a monoradical of an unsaturatedhydrocarbon, preferably having from 2 to 20 carbon atoms, morepreferably 2 to 10 carbon atoms and even more preferably 2 to 6 carbonatoms and having at least 1 and preferably from 1 to 6 sites ofacetylene (triple bond) unsaturation. Preferred alkynyl groups includeethynyl, (—C≡CH), propargyl (or prop-1-yn-3-yl, —CH₂C≡CH), and the like.In the event that alkynyl is attached to nitrogen, the triple bondcannot be alpha to the nitrogen.

The term “substituted alkynyl” refers to an alkynyl group as definedabove having from 1 to 5 substituents, and preferably 1 to 3substituents, selected from the group consisting of alkyl, alkenyl,alkynyl, alkoxy, cycloalkyl, cycloalkenyl, acyl, acylamino, acyloxy,amino, aminocarbonyl, alkoxycarbonylamino, azido, cyano, halogen,hydroxy, keto, thiocarbonyl, carboxy, carboxyalkyl, arylthio,heteroarylthio, heterocyclylthio, thiol, alkylthio, aryl, aryloxy,heteroaryl, aminosulfonyl, aminocarbonylamino, aminothiocarbonylamino,heteroaryloxy, heterocyclyl, heterocyclooxy, hydroxyamino, alkoxyamino,nitro, —SO-alkyl, —SO-aryl, —SO-heteroaryl, —SO₂-alkyl, SO₂-aryl and—SO₂-heteroaryl. All substituents may be optionally further substitutedby alkyl, alkoxy, halogen, CF₃, amino, substituted amino, cyano, or—S(O)_(n)R, in which R is alkyl, aryl, or heteroaryl and n is 0, 1 or 2.

The term “aryl” refers to an aromatic carbocyclic group of 6 to 20carbon atoms having a single ring (e.g., phenyl) or multiple rings(e.g., biphenyl), or multiple condensed (fused) rings (e.g., naphthyl oranthryl). Preferred aryls include phenyl, naphthyl and the like.

Unless otherwise constrained by the definition for the aryl substituent,such aryl groups can optionally be substituted with from 1 to 5substituents, preferably 1 to 3 substituents, selected from the groupconsisting of alkyl, alkenyl, alkynyl, alkoxy, cycloalkyl, cycloalkenyl,acyl, acylamino, acyloxy, amino, aminocarbonyl, alkoxycarbonylamino,azido, cyano, halogen, hydroxy, keto, thiocarbonyl, carboxy,carboxyalkyl, arylthio, heteroarylthio, heterocyclylthio, thiol,alkylthio, aryl, aryloxy, heteroaryl, aminosulfonyl, aminocarbonylamino,aminothiocarbonylamino, heteroaryloxy, heterocyclyl, heterocyclooxy,hydroxyamino, alkoxyamino, nitro, —SO-alkyl, —SO-aryl, —SO-heteroaryl,—SO₂-alkyl, SO₂-aryl and —SO₂-heteroaryl. All substituents may beoptionally further substituted by alkyl, alkoxy, halogen, CF₃, amino,substituted amino, cyano, or —S(O)_(n)R, in which R is alkyl, aryl, orheteroaryl and n is 0, 1 or 2.

The term “aryloxy” refers to the group aryl-O— wherein the aryl group isas defined above, and includes optionally substituted aryl groups asalso defined above. The term “arylthio” refers to the group R—S—, whereR is as defined for aryl.

The term “amino” refers to the group —NH₂.

The term “substituted amino” refers to the group —NRR where each R isindependently selected from the group consisting of hydrogen, alkyl,cycloalkyl, carboxyalkyl (for example, benzyloxycarbonyl), aryl,heteroaryl and heterocyclyl provided that both R groups are nothydrogen, or a group —Y-Z, in which Y is optionally substituted alkyleneand Z is alkenyl, cycloalkenyl, or alkynyl, All substituents may beoptionally further substituted by alkyl, alkoxy, halogen, CF₃, amino,substituted amino, cyano, or —S(O)_(n)R, in which R is alkyl, aryl, orheteroaryl and n is 0, 1 or 2.

The term “halogen” or “halo” refers to fluoro, bromo, chloro, or iodo.

The term “acyl” denotes a group —C(O)R, in which R is hydrogen,optionally substituted alkyl, optionally substituted cycloalkyl,optionally substituted heterocyclyl, optionally substituted aryl, oroptionally substituted heteroaryl.

The term “heteroaryl” refers to an aromatic group (i.e., unsaturated)comprising 1 to 15 carbon atoms and 1 to 4 heteroatoms selected fromoxygen, nitrogen and sulfur within at least one ring.

Unless otherwise constrained by the definition for the heteroarylsubstituent, such heteroaryl groups can be optionally substituted with 1to 5 substituents, preferably 1 to 3 substituents selected from thegroup consisting of alkyl, alkenyl, alkynyl, alkoxy, cycloalkyl,cycloalkenyl, acyl, acylamino, acyloxy, amino, aminocarbonyl,alkoxycarbonylamino, azido, cyano, halogen, hydroxy, keto, thiocarbonyl,carboxy, carboxyalkyl, arylthio, heteroarylthio, heterocyclylthio,thiol, alkylthio, aryl, aryloxy, heteroaryl, aminosulfonyl,aminocarbonylamino, aminothiocarbonylamino, heteroaryloxy, heterocyclyl,heterocyclooxy, hydroxyamino, alkoxyamino, nitro, —SO-alkyl, —SO-aryl,—SO-heteroaryl, —SO₂-alkyl, SO₂-aryl and —SO₂-heteroaryl. Allsubstituents may be optionally further substituted by alkyl, alkoxy,halogen, CF₃, amino, substituted amino, cyano, or —S(O)_(n)R, in which Ris alkyl, aryl, or heteroaryl and n is 0, 1 or 2. Such heteroaryl groupscan have a single ring (e.g., pyridyl or furyl) or multiple condensedrings (e.g., indolizinyl, benzothiazolyl, or benzothienyl). Examples ofnitrogen heterocycles and heteroaryls include, but are not limited to,pyrrole, imidazole, pyrazole, pyridine, pyrazine, pyrimidine,pyridazine, indolizine, isoindole, indole, indazole, purine,quinolizine, isoquinoline, quinoline, phthalazine, naphthylpyridine,quinoxaline, quinazoline, cinnoline, pteridine, carbazole, carboline,phenanthridine, acridine, phenanthroline, isothiazole, phenazine,isoxazole, phenoxazine, phenothiazine, imidazolidine, imidazoline, andthe like as well as N-alkoxy-nitrogen containing heteroaryl compounds.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where said event or circumstance occurs and instances in whichit does not.

The term “homopolymer” means a polymer derived from one species ofmonomer.

The term “copolymer” means a polymer derived from more than one speciesof monomer.

The term “statistical copolymer” means a copolymer consisting ofmacromolecules in which the sequential distribution of the monomericunits obeys known statistical laws, e.g. the sequential distribution ofmonomer units follows Markovian statistics.

The term “block copolymer” means a polymer composed of macromoleculesconsisting of a linear sequence of blocks, wherein the term “block”means a portion of macromolecule comprising many constitutional unitsthat has at least one feature which is not present in the adjacentportions.

The term “polymer matrix” refers to all of the polymer layers orsublayers on the metal surface. This can include activating, binding,container, and/or barrier layers.

The term “amphiphilic copolymer” means a polymer containing bothhydrophilic (water-soluble) and hydrophobic (water-insoluble) segments.

The term “polyester” means a polymer with structural units connected byester bonds, comprising polyesters obtained from dicarboxylic acids anddiols, or from hydroxyalkanoic acids by polycondensation, and includespolylactones obtained by ring-opening polymerization of lactones, suchas polyglycolides polylactides, polycaprolactone and related copolymers.

The term “metal” means surfaces made of, for example, stainless steel,titanium or tantalum with oxide groups on their surface, as well asother surfaces made of, for example, polymers or glass, with hydroxylgroups or other functional groups that can be transformed to hydroxylgroups on their surfaces. The surface may be of any shape and may be apart of any medical devices. Examples of such devices include bothimplantable or extracorporeal devices such as vascular graft tubing,blood oxygenators, intravascular balloons, catheters, implantable pulsegenerators, electrodes, electrical leads, stents, sutures, soft or hardtissue prosthesis, artificial organs and the like. Further, there arelikely to be many applications for the coated metal outside the medicalfield. Accordingly, it will be appreciated by those skilled in the artthat the invention described may be applied to many medical devices andin fields outside of medicine where a polymer coated metal surface ofthe invention may be useful.

A coating composition of this invention is preferably used to coat animplantable medical device that undergoes flexion or expansion in thecourse of its implantation or use in vivo. The words “flexion” and“expansion” as used herein with regard to implantable devices will referto a device, or portion thereof, that is bent (e.g., by at least about30 degrees or more) and/or expanded (e.g., to greater than its initialdimension), either in the course of its placement, or thereafter in thecourse of its uses in vivo.

Stents are designed to mechanically prevent the collapse and reocclusionof the coronary arteries. The coating composition can also be used tocoat stents, which are typically prepared from materials such asstainless steel or tantalum. A variety of stent configurations are knownincluding but not limited to shape memory alloy stents, expandablestents and stents formed in situ e.g., either self-expanding stents(such as the Wallstent variety), or balloon-expandable stents (as areavailable in a variety of styles, for instance, Gianturco-Roubin,Palmaz-Shatz, Wiktor, Strecker, ACS Multi-Link, Cordis, AVE MicroStent). Other suitable metals for such stents include gold,molybdenum-rhenuim alloy, platinum-iridium alloy and combinationsthereof. See, for example, U.S. Pat. No. 4,733,655, U.S. Pat. No.4,800,882 and U.S. Pat. No. 4,886,062, all of which are incorporated byreference in their entirety.

The polymer coating or coating composition on the metal surface can becomposed of several layers. Referring now to FIG. 1, the metal surfacehas a first coat (shown as A in FIG. 1), referred to herein as the metalactivating layer that is composed of silane polymer derivativescovalently bound to the metal surface. A second layer (shown as B inFIG. 1), referred to herein as the binding layer, is composed of apolylactone covalently bonded to the chemical groupings provided by thesilane polymer in the metal activating layer. A third layer (shown asC(1) in FIG. 1), referred to herein as the container layer, is depositedon the surface of the binding layer. The container layer may optionallybe composed of one or more sublayers of the same or different polymers.The binding layer and the coating layer may optionally contain one ormore biologically active compounds releasably dispersed in the polymermatrix. Once the coated metal surface is placed in an aqueousenvironment, typically the body fluids, such as blood, lymph orextracellular fluids, the biologically active compounds are releasedinto the aqueous environment. The composition of the binding layer andthe container layer may, for example, be adjusted to provide for acontrolled release of these compounds into a surrounding aqueous mediumand/or to modify the tissue reaction to the presence of the device, forexample, to make the surface thromboresistant. The coated metal surfacemay be composed of two or more sublayers with different functions,optionally the uppermost layer may function as a barrier or skin layer(shown as C(2) in FIG. 1).

The barrier or skin layer can be used to control the biologically activeagent release from the polymer matrix. For example, if a single polymermatrix container layer is formed on the surface, a skin layer of thesame polymer that is used in the container layer can be added on top ofthe container layer. This skin layer could either not contain abiologically active agent, or could contain a much lower biologicallyactive agent loading than is present in the container layer, and thuswould function as a diffusion barrier for the biologically active agent.

The skin layer can also have different properties, for example,crystallinity, or solubility in solvents, from the container layer.Thus, it may be possible to apply a skin layer using solvents that donot dissolve the underlying container layer and/or extract theincorporated biologically active agent.

A skin layer made of a hydrophobic polymer can provide better releasecontrol for hydrophilic biologically active agents (or agents with highsolubility in water) than a hydrophilic skin. A hydrophilic polymer inthe skin layer would facilitate uptake of water into the containerlayer, increase the hydration, concentration of soluble fraction and,consequently, make the release faster. On the other hand, the agentloading in the container layer is high, close to the percolation limit,a single hydrophilic skin layer may not provide sufficient releasecontrol.

The outermost skin or barrier layer can comprise more than one sublayer.The innermost sublayer of the skin layer can be hydrophobic. There maybe a hydrophilic sublayer on the outside of the innermost skin sublayerwhich would provide a biocompatible, nonadsorptive or otherwisebiospecific interface between the device and the tissue environment intowhich the device is placed.

The biologically active (e.g., pharmaceutical) agents useful in thepresent invention include virtually any therapeutic substance whichpossesses desirable therapeutic characteristics for application to theimplant site. As used herein “biologically active agent” refers to asingle biologically active agent or several biologically active agents.It is contemplated that one or more biologically active agents may bereleasably associated with the polymers on the metal surface. Theseagents include, but are not limited to: thrombin inhibitors,antithrombogenic agents, thrombolytic agents (e.g. factor Xainhibitors), fibrinolytic agents, vasospasm inhibitors, calcium channelblockers, vasodilators, antihypertensive agents, antimicrombial agents,antibiotics, inhibitors of surface glycoprotein receptors, antiplateletagents, antimitotics, microtubule inhibitors, anti secretory agents,actin inhibitors, remodeling inhibitors, antisense nucleotide, antimetabolites, antiproliferatives (e.g. E2F antisense compounds, Rapamycin(sirolimus), tacrolimus, Taxol, paclitaxol, Cyclin Dependent Kinaseinhibitors) anticancer chemotherapeutic agents, anti-inflammatorysteroid or non-steroidal anti-inflammatory agents, immunosuppressiveagents, growth hormone antagonists (e.g. PDGF receptor tyrosine kinaseinhibitors), growth factors, dopamine agonists, radiotheraputic agents,peptides, proteins, enzymes, extracellular matrix components, ACEinhibitors, free radical scavengers, chelators, antioxidants,antipolyermases, ribozymes, antiviral agents, photodynamic therapyagents, and gene therapy agents.

A preferred biologically active agent is a compound of the followingformula:

This compound, an anti-proliferative agent known generally as CVT 313,is named2-{(2-hydroxyethyl)-[9-isopropyl-6-(4-methoxybenzylamino)-9H-purin-2-yl]-amino}-ethanolor also known as2-diethanolamino-6-(4-methoxybenzylamino)-9-isopropylpurine. It isdescribed in U.S. Pat. No. 5,866,702, which is incorporated by referenceherein in its entirety.

Other compounds within the scope of either WO/08/05335 or WO/00/44750,both of which are incorporated herein in their entireties, include

-   2-[[6-(4-cholorbenzylamino)-9-isopropyl-9H-purin-2-yl]-(2-hydroxyethyl)-amino]-ethanol,    also known as    6-(4-chlorobenzylamino)-[bis-(2-hydroxyethylamino)]-9-isopropylpurine;-   N²-(2-aminoethyl)-N⁶-(4-chlorobenzyl)-9-isopropyl-9H-purine-2,6-diamine,    also known as    2-(2-aminoethylamino)-6-(4-chlorobenzylamino)-9-isopropylpurine;-   2-[[6-(2,5-diflurorbenzylamino)-9-isopropyl-9H-purin-2-yl]-(2-hydroxyethyl)-amino]-ethanol,    also known as    6-[(2,5-difluorophenyl)methylamino]-2-[bis-(2-hydroxyethylamino)]-9-isopropylpurine;-   2-[6-(2,5-difluoror-benzylamino)-9-isopropyl-9H-purin-2-ylamino]-3-methyl-butan-1-ol,    also known as    6-[(2,5-difluororphenyl)methylamino]-2-(1-hydroxymethyl-2-methylethylamino)-9-isopropylpurine;-   2-{[6-(4-bromophenylamino)-9-isopropyl-9H-purin-2-yl]-(2-hydroxyethyl)-amino}-ethanol,    also known as    6-4-bromophenylamino)-2-[bis-(2-hydroxyethylamino)]-9-isopropylpurine;-   2-{(2-hydroxyethyl)-[9-isopropyl-6-(quinolin-3-ylamino)-9H-purin-2-yl]-amino}-ethanol,    also known as    6-(quinolin-3-ylamino)-2-[bis-(2-hydroxyethylamino)]-9-isopropylpurine;-   N²-(2-aminopropyl)-N⁶-(4-chlorobenzyl)-9-isopropyl-9H-purine-2,6-diamine,    also known as    2-(2-aminopropylamino)-6-(4-chlorobenzylamino)-9-isopropylpurine;    and-   3-{[2-(2-aminoethylamino)-9-isopropyl-9H-purin-6-ylamino]-methyl}-benzoic    acid.

Other preferred biologically active agents are adenosine A2a receptoragonists which are known to increase endothelial cell migration andprevent smooth muscle cell growth. Examples of these compounds arerepresented by the following formulae and are described in detail in thereferenced patents and patent applications, each of which isincorporated by reference herein in its entirety.

WO 0078779

Known as(1-{9-[(4S,2R,3R,5R)-3,4-dihydroxy-5-(hydroxymethyl)-oxolan-2-yl]-6-aminopurin-2-yl}pyrazol-4N-propylcarboxamide,also known as 2-(4-propylaminocarbonylpyrazol-1-yl)adenosine WO 0078779

Known as(1-{9-[(4S,2R,3R,5R)-3,4-dihydroxy-5-(hydroxymethyl)-oxolan-2-yl]-6-aminopurin-2-yl}pyrazol-4N-methylcarboxamide,also known as 2-(4-methylaminocarbonylpyrazol-1-yl)adenosine

U.S. Pat. No. 6,214,807

Known as(4S,2R,3R,5R)-2-{6-amino-2-[1-benzylpyrazol-4-yl]purin-9-yl}-5-(hydroxymethyl)oxolane-3,4-diol;

U.S. Pat. No. 6,180,615

Known as(4S,2R,3R,5R)-2-[6-amino-2-(3-phenoxyprop-1-ynyl)-purin-9-yl]-5-(hydroxymethyl)-oxolane-3,4-diol;and WO 00/78776

The substituents for the above structure from WO 00/78776 have thefollowing definitions:

wherein X is S, O and NR⁵;

R¹ is —CH₂OH, and —C(═O)NR⁷R⁸;

R², R³, R⁴ and R⁵ are each individually selected from the groupconsisting of hydrogen, halo, NO₂, CF₃, CN, OR²⁰, SR²⁰, N(R²⁰)₂,S(O)R²², SO₂R²², SO₂N(R²⁰)₂, SO₂NR²⁰COR²², SO₂NR²⁰CO₂R²²,SO₂NR²⁰CON(R²⁰, N(R²⁰)₂ NR²⁰COR²², NR²⁰CO₂R²², NR²⁰CON(R²⁰)₂,NR²⁰C(NR²⁰)NHR²³, COR²⁰, CO₂R²⁰, CON(R²⁰)₂, CONR²⁰SO₂R²², NR²⁰SO₂R²²,SO₂NR²⁰CO₂R²², OCONR²⁰SO₂R²², OC(O)R²⁰, C(O)OCH₂OC(O)R²⁰, OCON(R²⁰)₂,C₁₋₁₅ alkyl, C₂₋₁₅ alkenyl, C₂₋₁₅ alkynyl, heterocyclyl, aryl, andheteroaryl, which alkyl, alkenyl, alkynyl, C₁₋₁₅ alkoxy, aryl,heterocyclyl, and heteroaryl are optionally substituted with from 1 to 3substituents independently selected from the group consisting of halo,NO₂, heterocyclyl, aryl, heteroaryl, CF₃, CN, OR²⁰, SR²⁰, N(R²⁰)₂,S(O)R²², SO₂R²², SO₂N(R²⁰)₂, SO₂NR²⁰COR²², SO₂NR²⁰CO₂R²²,SO₂NR²⁰CON(R²⁰)₂, N(R²⁰)₂NR²⁰COR²², NR²⁰CO₂R²², NR²⁰CON(R²⁰)₂,NR²⁰C(NR²⁰)NHR²³, COR²⁰, CO₂R²⁰, CON(R²⁰)₂, CONR²⁰SO₂R²², NR²⁰SO₂R²²,SO₂NR²⁰CO₂R²², OCONR²⁰SO₂R²², OC(O)R²⁰, C(O)OCH₂OC(O)R²⁰, and OCON(R²⁰)₂and wherein each optional heteroaryl, aryl, and heterocyclylsubstitution substituent is further optionally substituted with halo,NO₂, alkyl, CF₃, amino, mono- or di-alkylamino, alkyl or aryl orheteroaryl amide, NCOR²², NR²⁰SO₂R²², COR²⁰, CO₂R²⁰, CON(R²⁰)₂,NR²⁰CON(R²⁰)₂, OC(O)R²⁰, OC(O)N(R²⁰)₂, SR²⁰, S(O)R²², SO₂R²²,SO₂N(R²⁰)₂, CN, or OR²⁰;

R⁷ and R⁸ are each independently selected from H, and C₁₋₁₅ alkyloptionally substituted with from 1 to 2 substituents independentlyselected from the group consisting of halo, NO₂, heterocyclyl, aryl,heteroaryl, CF₃, CN, OR²⁰, SR²⁰, N(R²⁰)₂, S(O)R²², SO₂R²², SO₂N(R²⁰)₂,SO₂NR²⁰COR²² SO₂NR²⁰CO₂R²², SO₂NR²⁰CON(R²⁰)₂, N(R²⁰)₂ NR²⁰COR²²,NR²⁰CO₂R²², NR²⁰CON(R²⁰)₂, NR²⁰C(NR²⁰)NHR²³, COR²⁰, CO₂R²⁰, CON(R²⁰)₂,CONR²⁰SO₂R²², NR²⁰SO₂R²², SO₂R²⁰COR²², OCONR²⁰SO₂R²², OC(O)R²⁰,C(O)OCH₂OC(O)R²⁰, and OCON(R²⁰)₂ and each optional heteroaryl, aryl, andheterocyclyl substituent is further optionally substituted with halo,NO₂, alkyl, CF₃, amino, monoalkylamino or dialkylamino, alkylamide,arylamide or heteroarylamide, NCOR²², NR²⁰SO₂R²², COR²⁰, CO₂R²⁰,CON(R²⁰)₂, NR²⁰CON(R²⁰)₂, OC(O)R²⁰, OC(O)N(R²⁰)₂, SR²⁰, S(O)R²², SO₂R²²,SO₂N(R²⁰)₂, CN, and OR²⁰;

R²⁰ is selected from the group consisting of H, C₁₋₁₅ alkyl, C₂₋₁₅alkenyl, C₂₋₁₅ alkynyl, heterocyclyl, aryl, and heteroaryl, which alkyl,alkenyl, alkynyl, heterocyclyl, aryl, and heteroaryl are each optionallysubstituted with from 1 to 3 substituents independently selected fromhalo, alkyl, mono- or dialkylamino, alkyl or aryl or heteroaryl amide,CN, O—C₁₋₆ alkyl, CF₃, aryl, and heteroaryl; and

R²² is selected from the group consisting of C₁₋₁₅ alkyl, C₂₋₁₅ alkenyl,C₂₋₁₅ alkynyl, heterocyclyl, aryl, and heteroaryl which alkyl, alkenyl,alkynyl, heterocyclyl, aryl, and heteroaryl are each optionallysubstituted with from 1 to 3 substituents independently selected fromhalo, alkyl, mono- or dialkylamino, alkyl or aryl or heteroaryl amide,CN, —O—C₁₋₆ alkyl, CF₃, and heteroaryl.

In a preferred embodiment, the invention provides for the formation ofthe binding layer covalently bonded, grafted, or attached, to the metalactivating layer. The grafted polymer binding layer is formed by thein-situ ring opening polymerization of lactone monomers initiated bysuitable functional groups of the polymer of the metal activating layerand a catalyst added to the polymerization reaction.

Suitable functional groups for initiating the grafting polymerization oflactones (“initiating functional groups”) can be created on metalsurfaces through the reaction of a metal surface with selected silanederivatives, referred to herein as silane-based activating reagents(“SAR” or “SARs”). SAR is a silane derivative of general formula(R²)₃—SiR¹ wherein R¹ is independently selected from substituted alkyl,substituted alkenyl, substituted alkynyl, substituted aralkyl,substituted heteroaryl, and substituted alkoxy with the proviso that R¹contains a hydroxy or amino group, or a functional group that can betransformed to a radical that contains a hydroxy or amino group; whereinR² is independently selected from halo, optionally substituted alkoxy,optionally substituted aryloxy, optionally substituted silyloxy, oroptionally substituted alkyl with the proviso that all three R²substituents are not simultaneously substituted alkyl.

Typical SARs can be selected from alkoxysilane derivatives such astetraalkoxysilanes and organo-trialkoxysilane derivatives. Examples oftetraalkoxysilanes are alkoxysilanes of the formula Si(OR)₄ in which theR represents a C₁ to C₄ alkyl group, such as tetramethoxysilane,tetraethoxysilane, tetra-n-propoxysilane, tetra-n-butoxysilane, andanalogues. Typical examples of organo-trialkylsilanes are compounds of ageneral formula R′—Si—(OR)₃ in which the R represents C₁ to C₄ alkylgroups, and the R′ represents a non-hydrolyzable organic substituent.

Also, alkoxysilane derivatives acting as SARs can be formed in situ bythe reaction of halosilane derivatives with alcohols. Examples ofsuitable halosilanes effective in this mode will includetetrachlorosilane, trichloroalkyl silanes and dichlorodialkyl silanes.It becomes obvious that in this mode, the actual SAR is composed of amixture of chemical species that, in addition to the original halosilaneused, will contain tetraalkoxysilanes, trialkoxysilanes as well asdialkoxydialkyl silanes. The silicone industry offers a number ofvarious halosilane and haloalkylsilane as well as tetralkoxy- andorgano-trialkoxy-silane derivatives, and many possibilities exist forthe organic substituents. See, for example, GELEST Catalogue 2000:Silanes, Silicones and Metal-Organics. Gelest, Inc., Dr. Barry Arkles,Tullytown, Pa., USA.

Several structural features of SARs are important to the presentinvention. It is known that alkoxy groups of alkoxysilanes easilyundergo hydrolysis in the presence of water to form silanol groups.Subsequent condensation of silanol groups produces siloxane fromsilanols. It is also known that through condensation, silanol groupsform siloxane chains. Analogously, without wishing to be bound by anytheory, it is hypothesized that through the reaction of silanol groupswith surface hydroxyl groups of hydrated metal oxides, siloxane bondsbetween the silicone and metal atoms are formed, thus binding the silanemolecules to the surface. At the same time the other alkoxysilane bondsundergo hydrolysis-condensation reaction between silane molecules, thusleading to oligomerization and polymerization of silane and forming atwo or three dimensional siloxane network. A schematic representation ofthe mechanism and structure involved in the reactive adsorption ofalkoxysilane SARs on surfaces containing metal oxide groups is shown inFIG. 2. A metal oxide surface comprising metal atoms M having hydroxylsubstituents OH is reacted with a SAR having the formula R′—Si(OR)₃.Following the removal of water from the reaction, the SAR is covalentlybound to the metal surface. In addition, the SAR provides an initiatingfunctional group, such as an alkanol or hydroxyalkyl group, for theinitiation of in-situ polymerization of a polyester to provide thebinding layer on the metal surface.

While FIG. 2 shows the hydrolysis/condensation reaction achieving thesiloxane activating layer as a two dimensional (monomolecular) layer, itis expected that the hydrolytic polymerization of a SAR producesoligomeric species of three-dimensional, cyclic and cross-linkedaggregates that interact with the metal surface to provide the siloxaneactivating layer. Therefore, it is expected that the cross-linkedpolymerized structure of the siloxane layer has multiple attachmentpoints with the metal, that results in the siloxane layer being firmlyadhered to the metal surface.

Suitable functional groups for R′ are hydroxyalkyl groups that can formalkoxides through the reaction with a metal catalyst. In this way, thesiloxane activating layer with free hydroxyalkyl groups can be preparedby using functional trialkoxysilanes as SAR. Examples of suitabletrialkoxysilanes include hydroxyalkyl alkoxysilane derivatives. Inaddition, the following are examples of commercially availablesilane-based activating reagents that contain a hydroxy group:N-(3-triethoxysilylpropyl)-4-hydroxybutyramide,N-(3-triethoxysilylpropyl)gluconamide,3-[Bis(2-hydroxyethyl)amino]propyl-trimethoxysilane, and3-[Bis(2-hydroxyethyl)amino]propyl-triethoxysilane.

In addition to alkanol and hydroxyalkyl groups, the polymerization oflactones in the presence of suitable metal catalysts can be efficientlyinitiated also by other strong nucleophiles, in particular by amines,including primary alkyl amines, sterically unhindered secondary aminesand compounds containing a nucleophilic amino alkyl chain. Under certainconditions, the reaction of amines with lactones is fast enough toinitiate polymerization of lactones in solution or melt. The initialreaction of the amine with lactones, such as lactide, glycolide orε-caprolactone, provides for amides having an ω-hydroxyalkyl group, suchas lactoyllactyl amide, glycolylglycylamide or 6-hydroxycaproyl amide,respectively. Through their ω-hydroxyalkyl groups these amides can formalkoxides with a suitable metal catalyst and in presence of anadditional lactone monomer (monomer is defined to include the cyclicdimers of lactic acid and glycolic acid as well as other cylic lactonemonomers), polymerization can continue by a propagation reaction,typical for lactone ring-opening polymerization. Suitable reactionconditions for the initiation of the lactone polymerization byalkylamine groups on the surfaces are well compliant with those requiredfor lactone polymerization in general. These conditions includeexclusion of water and other protic compounds from the system, exceptthe protic groups presented by activated surface, either in solution ora melt. Typically, an elevated temperature would be beneficial, as itincreases the reaction rate of amine and lactone species and theformation of amide bonds. Typical temperature range will be 20 to 250°C., preferrably 20 to 120° C., for solution reactions, with the upperlimit of this range depending on the solvent and the decompositiontemperature of the lactone, while the minimum temperature of thereaction in bulk or a lactone melt will be dependent on the meltingtemperature of selected lactone monomer.

Thus, the lactone polymerization can be efficiently initiated by theaminoalkyl groups present in the surface activating layer. This allowsfor the formation of grafting-susceptible functional groups at the metalsurfaces by using silane-based activating agents with an amino group.Typical examples of commercially available reagents that may be usefulas SARs to be applied in this way include

-   N-(3-aminoethyl)-3-aminopropyltrimethoxysilane,-   3-aminopropyl-trimethoxysilane,-   3-aminopropyltriethoxylsilane,-   methyl(2-(3-trimethoxysilylpropylamino)-3-propionate,-   3-(N-styrylmethyl-3-aminoethylamino)-propyl-trimethoxysilane    hydrochloride,-   4-aminobutyltriethoxysilane,-   3-(3-aminopropoxy)3,3-dimethyl-1-propenyltrimethoxysilane,-   N-(6-aminohexyl)aminopropyltrimethoxysilane,-   N-(3-trimethoxysilylethyl)ethylenediamine,-   N-(2-(N-vinylbenzylamino)ethyl)-3-aminopropyltrimethoxysilane    hydrochloride,-   1-trimethoxysilyl-2-(aminomethyl)phenylethane,-   N-2-(aminoethyl)-3-aminopropyltris-(2-ethyloxy)silane,-   3-(N-allylamino)propyltrimethoxysilane,-   3-(2-aminoethylamino)propyltrimethoxysilane, and-   3-(2-aminoethylamino)propyltriethoxysilane.

In addition to using alkoxy silane and amino silane derivatives toderivatize a metal surface, the same result can be achieved by usingreactive alkoxysilane intermediates containing a functionalized alkylgroup that can be converted to hydroxyalkyl or an amino alkyl groupthrough a subsequent modification reaction with nucleophiles. Typicalexamples of suitable silylating reactants useful for this mode of theprocedure include

-   (3-isocyanatopropyl)triethoxysilane,-   (3-thioisocyanatopropyl)triethoxysilane,-   (3-glycidyloxypropyl)trimethoxysilane,-   (3-glycidyloxypropyl)triethoxysilane,-   (3-bromopropyl)trimethoxysilane, chloropropyl)trimethoxysilane and    analogous compounds.

The isocyanate, thiocyanate, glycidyl or haloalkyl groups present inthese reagents can be used for introduction of hydroxyalkyl and/or aminegroups by their reaction with diols, amino alcohols, amines and/ordiamines. Analogously, alkenyl alkoxysilanes, containing an unsaturatedbond in their alkenyl chain, such as allyltrialkoxysilanes,(6-hexen-1-yl)trialkoxysilanes, (7-Octen-1-yl)trialkoxysilanes andanalogues, can be modified by the reaction with sulphanyl alkanols andsulphanyl amines. These and other analogous reactions are known to thoseskilled in the art and are consistent with the scope of the invention.

The following are commercially available reagents that contain afunctional group that can be activated to a hydroxy group or amino groupthrough a chemical transformation and which may be useful and silanebased activating reagents:

-   3-chloropropyltrimethoxysilane,-   3-mercaptopropyltrimethoxysilane,-   3-glycidoxypropyltrimethoxysilane,-   vinyltris(2-methoxyethoxy)silane,-   vinyltrimethoxysilane,-   vinyltriethoxysilane,-   allyltriethoxysilane,-   2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,-   3-chloropropyltriethoxysilane,-   2-cyanoethyltriethoxysilane,-   3-cyanopropyltrimethoxysilane,-   vinyltriphenoxysilane,-   chloromethyltriethoxysilane,-   2-cyanoethyltrimethoxysilane,-   3-acetoxypropyltrimethoxysilane,-   3-thiocyanatopropyltriethoxysilane,-   3-isocyanatopropyltrimethoxysilane,-   (p-chloromethyl)phenyltrimethoxysilane,-   tetraallyloxysilane,-   triethoxysilylpropylethylcarbamate,-   allyltrimethoxysilane,-   3-bromopropyltrimethoxysilane,-   3-mercaptopropyltriethoxysilane,-   4-((chloromethyl)phenethyl)trimethoxysilane,-   2-carbethoxyethyltriethoxysilane,-   allyltris(trimethylsiloxy)silane,-   diethylphospatoethyltriethoxysilane,-   3-iodopropyltrimethoxysilane,-   8-bromooctyltrimethoxysilane,-   diethyl(triethoxysilylpropyl)malonate,-   1-methyl-4-(1-methyl-(2-triethoxysilyl)ethyl)-cyclohexene,-   3-butenyltriethoxysilane,-   4-(trimethoxysilyl)-1-butene,-   (2-(3-cyclohexenyl)ethyl)triethoxysilane,-   4-(trimethoxysilyl)butane-1,2-epoxide,-   2-(3,4-epoxycyclohexyl)ethyltriethoxysilane,-   triallyloxyvinylsilane,-   5-(bicycloheptenyl)triethoxysilane,-   acetoxymethyltriethoxysilane,-   acetoxymethyltrimethoxysilane,-   (p-chloromethyl)phenyl-tri-N-propoxysilane,-   3-(triethoxysilyl)-2-methylpropylsuccinic anhydride,-   2-(triethoxysilylethyl)-5-(chloroacetoxy)bicycloheptane,-   2-(chloromethyl)allyltrimethoxysilane,-   2-carboethoxytriethoxsilane,-   11-cyanoundecyltrimethoxysilane,-   5,6-epoxyhexyltriethoxysilane,-   mercaptomethyltrimethoxysilane,-   3-(N-cyclohexylamino)propyltrimethoxysilane,-   triethoxysilylpropylmaleamic acid,-   3-bromopropyltriethoxysilane,-   3-trifluoroacetoxypropyltrimethoxysilane,-   vinyltrichlorosilane,-   allyltrichlorosilane,-   (3-acetoxypropyl)trichlorosilane,-   3-chloropropyltrichlorosilane,-   3-cyanopropyltrichlorosilane,-   3-chloropropyltrichlorosilane,-   2-(carbomethoxy)ethyltrichlorosilane,-   acetoxyethyltrichlorosilane,-   3-bromopropyltrichlorosilane,-   7-octenyltrichlorosilane,-   [2-(3-cyclohexenyl)ethyl]trichlorosilane,-   (p-chloromethyl)phenyltrichlorosilane,-   2-chloroethylsilane,-   bicycloheptenyl-2-trichlorosilane,-   3-(trichlorosilyl)cyclopentene,-   (3-cyanobutyl)trichlorosilane,-   3-cyclohexenyltrichlorosilane,-   (chloromethyl)phenethyl)trichlorosilane,-   5-hexenyltrichlorosilane,-   2-(chloromethyl)allyltrichlorosilane,-   11-bromoundecyltrichlorosilane,-   p-(T-butyl)phenethyltrichlorosilane,-   2-(chloromethyl)propyltrichlorosilane,-   8-nonenyltrichlorosilane,-   10-undecenyltrichlorosilane,-   (4-cyclooctenyl)trichlorosilane,-   14-tetradec-1-enyltrichlorosilane,-   2-bromoethyltrichlorosilane,-   methacryloxypropyltris(methoxyethoxy)silane,-   methacryloxypropyltris(trimethylsiloxy)silane,-   3-methacryloxypropyltris(vinyldimethylsiloxy)silane,-   (3-acryloxypropyl)trimethoxysilane, and-   methacryloxypropyltriethoxysilane.

The modification reactions of reactive silane intermediates can beconveniently performed in conjunction with the silylation of the metalsurfaces. Accordingly, the silylation reaction is carried out with theSAR having a reactive silane intermediate in the presence ofnucleophiles such as diols, amino alcohols or amines. Otherwise, thesilylation reaction can be performed in one step and, subsequently, themodification with nucleophile reactants can be applied on the silylatedmetal surfaces.

To treat metal surfaces, the SAR can be applied in solution or in avapor phase. A variety of solvents and solvent compositions can be used.In this respect, numerous references are available, teaching the use ofsilane derivatives in sol-gel processes and as adhesion promoters incorrosion protection. For a review of this art see for example, Iler, R.K. The Chemistry of Silica, Wiley, New York, 1979; Brinker, C. J.,Scherer, G. W., Sol-Gel Science: the Physics and Chemistry of Sol-GelProcessing, Academic Press, New York, 1990; Jang, J., Kim, E. K.Corrosion Protection of Epoxy-Coated Steel Using Different SilaneCoupling Agents, J. Applied Polym. Sci. (1999), 71:585, each of which isincorporated herein by reference in its entirety.

It is expected that the siloxane polymer is bonded to the metal surfacethrough a siloxane bond to the oxygen atom of the metal oxide.Therefore, the presence of metal oxide on the surface is expected to beimportant. Most of the metal articles, due to their contact with air,already exhibit a layer of metal oxide on their surface, which would besufficient to carry out the procedure according to this invention.However, a treatment of the metal surface by an oxidizing agent prior toapplication of SAR, for example, the treatment of the metal surface byan oxidizing agent as a part of a cleansing procedure is consistent withthis invention.

The polymerization of alkoxysilane involves the hydrolysis of alkoxidesas one of the reaction steps. Therefore, the presence of water moleculesin the reaction medium is expected to be important. Accordingly, SAR maybe applied in a solution which contains water either addedintentionally, or present as an impurity, as it is common in commercialgrades of many solvents. Water can also be added to the system byletting it adsorb on the metal surface to be treated, either by exposingthe oxidized surface to the water vapors or, in some cases, the amountof water adsorbed from the air in contact with metal will be sufficient.

The polymerization of alkoxysilanes involves condensation reactionsincluding silanols, alkoxides and metal oxides, during which waterand/or alcohol molecules are liberated. Therefore, conditions enhancingthe removal of the leaving compounds may be employed. Such conditionsinclude treatment of silanized surfaces at elevated temperature or theapplication of a vacuum.

Following the silylation of the metal surface, a binding polymer layeris applied to the surface. To apply the polymer of the binding layer, abinding or grafting reaction is carried out by exposing theSAR-activated surface to a solution of lactone and the catalyst in asuitable aprotic solvent, or to a mixture of catalyst and a lactone inbulk. In the initiation reaction of the grafting polymerization, thefirst lactone monomer forms a covalent bond with the functional group ofthe SAR bound to the metal surface. In subsequent steps, the polylactonechain propagates by a stepwise addition of lactone monomer. Theresulting polymer molecules thus remain covalently bound to the surfacethrough its initial structural unit. The chemical mechanisms that applyin the polymerization grafting used in this embodiment are analogous tothose that apply in the ring-opening polymerization of lactones in bulkor a solution. The field of lactone polymerization either in bulk or asolution is well described in numerous literature and principles ofthese reactions are known to those, skilled in the art. Examples of themost frequently used polymerization reactions can be found in Dubois, P.et al., Aluminium Alkoxides: A Family of Versatile Initiators for theRing-Opening Polymerization of Lactones and Lactides, Makromol. Chem.,Macromol. Symp. (1991) 42/43:103-116; Inoue, S., CoordinationRing-Opening Polymerization. Prog. Polymer. Sci. (1988) 13:63-81; Jonte,J. M. et al., Polylactones. 4. Cationic Polymerization of Lactones byMeans of Alkylsulfonates. J. Macromol. Sci.-Chem. (1986) A23:495-514;Kricheldorf, H. R. et al., Anionic and Pseudoanionic Polymerization ofLactones—a Comparison. Makromol. Chem., Macromol. Symp. (1990),32:285-298; Kricheldorf, H. R. et al., Poly(Lactones). 9. PolymerizationMechanism of Metal Alkoxide Initiated Polymerizations of Lactide andVarious Lactones, Macromolecules (1988) 21:286-293; and Lofgren, A. etal., J. M. S.-Rev. Macromol. Chem. Phys. (1995) C35:379-418, each ofwhich are incorporated by reference in their entirely.

It is known that typical initiating species in lactone polymerizationare metal alkoxides which can be added to the reaction mixture or areformed in situ from the metal catalyst and alkanols or otherhydroxyl-containing compounds. According to a preferred embodiment ofthe invention, only the functional groups of the metal activating layerbound to the metal surface are to be involved in the initiation oflactone polymerization. Thus, during the initiation of the graftingpolymerization, the hydroxyl and/or amine groups present in the siloxanepolymer will become acylated by lactone monomer and, subsequently,through the continuing chain addition of monomer, the polyester chainwill grow anchored by its initial acyl bond to the siloxane functionalgroups. This method of polymerization is hereafter termed a graftingpolymerization.

Accordingly, in contrast to the usual lactone polymerization in bulk ora solution, it is preferred in the present invention that the additionof free species, that can act as initiating species of lactonepolymerization, into the polymerization medium is avoided. Theincidental presence of these compounds or protic impurities, which maylead to the formation of free initiating species in the medium, couldinitiate the growth of free polylactone polymers in the bulk (or asolution) which will not be bound to the surface. Such free polymerchains will be inefficient in formation of the binding layer, as theywould be easily washed out by a polymer solvent.

Suitable monomers in grafting polymerization are lactones. Typicalexamples of lactones include four to seven-membered lactones, forexample, the families of compounds comprising oxetan-2-one and4-alkyl-oxetan-2-one, dihydrofuran-2-one and 5-alkyl-dihydrofuran-2-one,tetrahydropyran-2-one and 6-alkyl-tetrahydropyran-2-one, oxepan-2-oneand 7-alkyl-oxepan-2-one, 1,4-dioxan-2,5-dione,3,6-alkyl-1,4-dioxan-2,5-dione, 1,3-dioxepan-2-one, 1,3-dioxan-2-one,1,3-dioxolan-2-one, 1,5-dioxepan-2-one, 1,4-dioxepan-2-one,1,3-dioxepan-4-one, and their substituted analogues, wherein the alkylis C1-C10 alkyl or a substituted alkyl. In a preferred embodiment of theinvention the lactone monomer comprises lactide(3,6-dimethyl-1,4-dioxane-2,5-dione) in its various enantiomeric forms(L-lactide, D-lactide, meso-lactide and their mixtures), glycolide(1,4-dioxane-2,5-dione), and ε-caprolactone.

For the binding layer, combinations of lactone monomers may be used toprovide for grafting copolymerization. These copolymers can be madeavailable with different ratios of the co-monomers. Both thehomopolymers and copolymers can be used in different molecular-weightranges. Preferably, the lactone copolymer includes one ofpoly(L-lactide-co-D-Lactide), poly(L-lactide-co-glycolide),poly(D-lactide-co-glycolide), poly(D,L-lactide-co-glycolide),poly(lactide-co-caprolactone), poly(lactide-co-dioxanone), andpoly(lactide-co-dioxepanone).

The grafting of lactone molecules onto the functional groups at thesurface can be carried out by applying the coordination-insertionmechanism of lactone polymerization. This method is particularlysuitable, because it does not involve strongly acidic or alkalineconditions or reactants. Therefore, the metal siloxane bonds of theactivating polysiloxane layer are preserved.

In the coordination-insertion mechanism, the polymerization processstarts by the reaction of hydroxyalkyl groups attached to the surfacewith a metal catalyst, thus leading to the formation of metal-alkoxideswith a covalent or coordination metal-oxygen bond and energeticallyfavorable free p- or d-orbitals. The coordination of the metal atom ofthe alkoxide with the oxygen of the lactone molecule leads to theweakening of the acyl bond of the lactone ring which, subsequently,opens and is inserted between the metal and oxyalkyl residue, thuspropagating the metal-alkoxide grouping. By repeating this step withother lactone molecules, the polymer chain propagates. Suitable metalcatalysts in this mechanism are metal carboxylates, alkyl metallic andhalide metallic compounds. Typical examples of suitable catalystsinclude tin(II), antimony, zinc, iron or calcium carboxylates,organo-aluminum and organo-tin compounds, tin, zinc, titanium,zirconium, ytterbium halides, etc. In general, the classes of catalyststhat can be used are generally known to those skilled in the art for thepolymerization of lactones in bulk or solution. In applications relatedto medical devices, non toxic and low-toxicity catalysts, such astin(II), zinc, calcium and iron carboxylates, and alkyl aluminumcompounds, are preferred. Examples of the preferred catalysts mayinclude tin(II) 2-ethyl hexanoate, tin(II) lactate, zinc(II)2-ethylhexanoate, zinc(II) lactate, triethyl aluminum anddiethylaluminum chloride.

Typical examples of aprotic solvents for carrying out the graftingreaction in solution include ethers (e.g., tetrahydrofuran, dioxane,di(ethylene glycol), diethyl ether), ketones (e.g. ethylmethyl ketone,diisobutyl ketone) and aromatic hydrocarbons (e.g. toluene, xylene), andmixtures of these solvents. Those skilled in the art can readilyidentify other solvents which would be useful for the grafting reaction.

The concentration of the lactone in the solution should be such thatthere is sufficient surplus of the mole amount of lactone over the moleamount of initiating functional groups on the activated metal surface tobe grafted. These conditions are easily achieved for a wide range oflactone concentrations. The preferred concentration of lactone is suchthat the mole amount of lactone is higher than the amount of surfacefunctional groups. More preferably, the mole amount of lactone should beat least ten times higher than the amount of surface functional groups.In practice, these conditions will be well achieved with the weightconcentration of lactone in the solution being in a range of 0.1 to 50%,typically, in a range of 0.1 to 10% (w/w).

The grafting reaction can be carried with a wide range of catalystconcentrations. It has been found that the most efficient mole amount ofthe catalyst is the mole amount equal to or higher than the mole amountof functional initiating groups on the surface to be grafted. The moleratio of the catalyst to lactone is not specifically limited. Theselection of a suitable mole ratio is guided by practical reasons andtype of catalyst used, taking into account possible toxicity of somecatalysts, that would call for minimizing the catalyst concentration onone hand, and the fact that the rate of polymerization increases withthe increasing catalyst/lactone ratio on the other. A preferredcatalyst-to-lactone mole ratio is in a range of 1/10 to 1/1000.

In addition, the grafting reaction can be carried out in the absence ofsolvent, i.e., in the mixture formed by a lactone in bulk and acatalyst. In this mode of the invention, the temperature of the reactionis preferably such as to keep the lactone in a liquid state, such asabove the melting temperature of the lactone. The reaction in lactonemelt is carried out for the time necessary to form a binding layer of adesired thickness. After carrying out the reaction for a given time, thesurface is removed from the melt, the residual lactone is washed fromthe surface by a suitable solvent and the grafted surface is dried.

The polylactone-grafted metal surfaces exhibit novel propertiesaffecting their surface energy, wettability, adsorptivity, and theirinteractions in the biological environments. Such interactions includeprotein adsorption, thrombogeneity, platelet adhesion and activation,and modified tissue reactions.

The covalently grafted polymer binding layer is firmly bonded to themetal surface. As a result of this covalent binding the grafted polymerlayer is resistant to removal by treatment with solvents. However,thermodynamically good solvents can penetrate into the grafted polymerlayer, causing the polymer chains to expand and thus become capable ofadsorbing or accumulating compounds from solutions. The adsorbed oraccumulated compounds can be either biologically active agents ormolecules of another polymer that have a similar or a compatiblechemical structure or that are miscible with the grafted polymer. Thesefeatures of the grafted polylactone layer can be employed either fordirect incorporation of biologically active agents to be released fromthe layer or for the design and attachment of other subsequent, welladherent, high-capacity polymer layers incorporating the agents.

When the polylactone binding layer grafted to the metal surface issoaked in a solution of the biologically active agent in a solventappropriate for a given polylactone, the solvent swells the graftedpolymer and makes it possible for the biologically active agent topenetrate the polymer layer. After the solvent is stripped off byevaporation, which can be either spontaneous or assisted by theapplication of vacuum, the biologically active agent, being lessvolatile than the solvent, is embedded in the polymer, the chains ofwhich have condensed, thus becoming closely packed into a compact matrixupon removal of solvent. Later, when the surface is put into anenvironment which is not a good solvent for the polymer, such as theaqueous environment of tissue fluids, the condensed polymer chainsprevent the molecules of the agent from being rapidly dissolved ordiffused into the aqueous medium. This action extends the time periodwithin which the agent is released.

According to a preferred embodiment of the invention, the polylactonebinding layer grafted to the metal surface is soaked in a solutionformed by a good solvent for polylactone, a biologically active agent,and a polymer that is chemically compatible or miscible with the graftedone. The polymer deposited from the solution on the top of the graftedbinding layer forms the container layer on the surface. When the surfaceis soaked in the solution, the solvent swells the grafted polymerbinding layer and the polymer molecules which are to form the containerlayer penetrate the swollen grafted binding layer and entangle with thegrafted chains. Additionally, the biologically active agent in solutionmay become embedded in the binding layer. In practice, the solutioncontaining the polymer of the container layer is applied to form aliquid film on the top of the grafted binding layer surface. After thesolvent has been evaporated from the solution, the solidified polymerfilm of the container layer will become well joined with the underlyinggrafted binding layer due to mutual entanglements of polymer chains.Layers of polymers of various controllable thickness and composition canbe applied to the anchoring grafted binding layer to form sublayers ofthe container layer. Biologically active agents contained in thesolution with the polymer remain embedded in the solidified polymercontainer layer film. It is also possible to soak the polylactonebinding layer grafted to the metal surface in a solution of abiologically active agent, using a good solvent for both the graftedpolylactone and the biologically active agent. The biologically activeagent will penetrate into the grafted polymer binding layer which isbeing swollen by the solvent and, after evaporation of the solvent, thebiologically active agent will then remain embedded in the graftedpolymer binding layer.

Biologically active agents can be released from the solidified film ofbinder and/or container layer into the aqueous environment by theirgradual dissolution and diffusion through the polymer matrix. Thisrelease may also be accomplished by polymer degradation alone, or inaddition to the diffusion of the biologically active agent through thepolymer matrix. By controlling the thickness and composition of thepolymer layers (e.g., binding and container), the capacity of the systemfor the loaded biologically active agent and the rate of its release canbe controlled. Accordingly, the biologically active agent is releasablyassociated with the polymer. When the coated metal surface is used as animplantable medical device, the biologically active agent can be locallyreleased from the polymer matrix in a controlled manner into a patientreceiving the medical device.

In one embodiment of the invention if lactide is used for grafting thebinding layer to the activated metal surface, a poly(lactide) serves asthe container layer. In this case, the same chemical structure ofpolymers in both the binding and container layers assures their goodadhesion. Analogously, when a poly(ε-caprolactone) layer is desired tobe the main component of the container layer, its good adhesion to thesurface can be achieved by using ε-caprolactone as a monomer in thegrafting polymerization of binding layer. Accordingly, a stable and welladherent polymer matrix can be achieved through various combinations ofthe compositions of the container layer and the binding layer using avariety of lactone polymers and copolymers by taking into account thechemical compatibility or miscibility of the polymers of both layers.

In various embodiments of the invention, the physical properties of thepolymer coating matrix can be modified while maintaining thecompatibility of the binding layer and the container layer. Thecomposition of the polymers in the layers can be adjusted by usingeither a chemical modification, such as statistical and blockcopolymers, or a physical modification, such as blends or composites.

The polymers used for formation of the container layer include lactonehomopolymers, examples of which include poly(L-lactide),poly(D-lactide), polyglycolide, poly(ε-caprolactone), poly(p-dioxanone,poly(dioxepanone), poly(trimethylene carbonate) statistical copolymersof lactones, examples of which may include poly(L-lactide-co-D-Lactide),poly(lactide-co-glycolide), poly(D,L-lactide),poly(lactide-co-caprolactone), poly(lactide-co-trimethylene carbonate)and other combinations of lactones that can be typically derived fromlactone monomers. These copolymers can be made with different ratios ofthe co-monomers. Both the homopolymers and copolymers can be used indifferent molecular-weight ranges.

The container layer can also include a block copolymer containing atleast one polylactone block. The other blocks of the copolymer can bebased on polylactone or another chemical structure such as polyether,poly(amino acid), poly(acrylate), poly(methacrylate), polybutadiene,polyisoprene, etc. Typical examples of compositions of suitable blockcopolymers comprise polylactide/polycaprolactone,polylactide/poly(ethylene oxide), polycaprolactone/polybutadiene,polycaprolactone/poly(ethylene oxide), polylactide/poly(amino acid). Theblock copolymers can exhibit different ratios of block lengths,different numbers of blocks, and different molecular weights.

It is anticipated that the properties of copolymers may vary withdifferent ratios of co-monomers in the copolymers as well as they mayvary with molecular weight. The invention is not limited to anyparticular copolymer composition or a molecular weight range. Inaddition to changing the chemical constitution of the polymer molecules,the properties of polymer films formed can be modified also by blendingdifferent types of polymers, i.e. homopolymers, statistical and blockcopolymers.

In the selection of solvent for the polymer of the container layer andthe biologically active agent, one has to take into account thesolubility of a given polymer composition in the solvent of choice.Typically the selection of solvent will vary with various types ofpolymers used for formation of the container layer. For instance, whenpolymers with low degree of crystallinity are used, such aspoly(D,L-lactide), and lactide copolymers, suitable solvents can bechosen from medium interactive solvents, comprising ethers, ketones,amides, aromatics and chlorinated hydrocarbons. Typical examples ofsuitable solvents include tetrahydrofuran, dioxane, toluene, acetone,N,N-dimethylformamide, dimethylsulfoxide, chloroform, dichloromethane,and dichloroethane, as well as mixed solvents comprising variouscombinations of these and other solvents. When polymers with high degreeof crystallinity are used, such as polyglycolide, poly(L-lactide) etc.,strongly interacting solvents, such as hexafluoropropanol ortrifluoroacetic acid, may be needed.

The selection of the solvent will also be made with respect to thesolubility of the biologically active agent to be incorporated.Depending on the type of biologically active agent, various approachescan be adopted. In one mode, the selected solvent may be a good solventfor both, the polymer and biologically active agent. In this approach,the mixture of the polymer and the biologically active agent will beapplied in a form of a homogenous solution. In another mode of theprocedure, a good solvent for the polymer, which, however, does notdissolve the biologically active agent, can be chosen. In this approachthe polymer-agent composition will be applied in a form of aheterogeneous suspension of the particles of the biologically activeagent in the polymer solution. It becomes apparent, that there can bevarious intermediate modes, in which the biologically active agent iseither only partly soluble in the selected solvent, or it reaches itssolubility limits during evaporation of the solvent after itsdeposition. The outcomes based on these considerations will influencethe phase structure and morphology of the biologically active agentdispersion in the container layer and, consequently, the parameterscontrolling the rate and duration of the biologically active agentrelease. The invention is not particularly limited to any of theseapproaches.

There are many ways to apply the polymer solution to become thecontainer layer on the polymer-grafted binding layer surface of a metalarticle. Procedures commonly known in coating applications can be usedas long as they provide for good wetting of the binding layer surface bythe polymer solution. Preferably the application procedure will allowfor the control of the parameters of the polymer layer such as layercomposition, thickness, and integrity. Thus, the polymer solution can beapplied on the binding layer surface by dipping the surface to be coatedin the polymer solution, by spraying the polymer solution on the bindinglayer surface, by pouring or spreading the solution onto the bindinglayer surface, or any other technique known to those skilled in the art.After the solution is applied to the binding layer surface, excesssolvent is evaporated. Various means to control the amount of solutionremaining on the binding layer surface before and during evaporation ofthe solvent can be used to control the thickness and homogeneity of thecontainer layer. These procedures include spreading the solution andstripping its excess by a centrifugal force, spreading and removing theexcess solution by a spreading tool, dosed spraying, and thoseprocedures that are generally known in the art of polymer coating.

In a preferred embodiment of the invention, the compositions of thegrafted binding layer and the container layer are chosen such that atleast one polymer component of the container layer is well compatiblewith the polymer of the binding layer. Compatibility between the layersimproves the wetting of the binding layer by the solution of thecontainer layer and facilitates the formation of a contiguous andwell-adherent polymer matrix. Thus, the polymer film of the containerlayer may be designed so that it has the desired composition, thicknessand physical properties, such as morphology, phase structure, glasstransition, and crystallinity, while being capable of being applied in asimple coating technique.

According to another embodiment of the invention, the polymer solutionof the container layer may contain one or more biologically activeagents that are intended to be released when a device with the polymermatrix is placed in an appropriate aqueous environment. The biologicallyactive agent may be either dissolved in the solution containing thepolymer, or it can be dispersed in the solution of the polymer in a formof solid particles. In either case, the biologically active agent willbecome incorporated in the polymer film during the solidification of thepolymer layer by solvent evaporation.

The rate of the release of the biologically active agent can becontrolled through the composition and other parameters of the polymercontainer layer. The parameters such as layer thickness, morphology,phase structure, hydrophobicity, degree of hydration, the ratio ofcrystalline and amorphous phases, glass-transition temperature of thepolymer are relevant to release control. These parameters can becontrolled through the selection of polymers and their applicationprocedures.

It is known that the stereoregular homopolymers, such as poly(L-lactide)or poly(D-lactide) exhibit a semicrystalline structure, with the contentof crystalline phase typically up to about 60 percent of the polymer. Inone mode of performing the invention, by using copolymers of D- andL-lactide and by changing the ratio of L and D stereoisomers, thecontent of the crystalline phase will change from a highly crystallinematerial for pure poly(L-lactide), or pure poly(D-lactide), to fullyamorphous material for the ratio of stereoisomers approaching 1:1. Sincethe diffusion of compounds within and out of the polymer matrix dependson the mobility and rotational freedom of polymer chains, which mobilityand rotational freedom are strongly hindered in the crystalline state ofthe material, the diffusion of biologically active agents through thecrystalline phase of the polymer matrix will be hindered. Thus, thevolume fraction of the crystalline phase in the polymer matrix willaffect diffusion of the biologically active agent. Therefore, therelease of the biologically active agent can be controlled by using apoly(L-lactide-co-D-lactide) in which the mole fraction of either of theL-lactide or D-lactide units in the copolymer is greater than about 0.7.This allows for the copolymer to maintain a semicrystalline structureand inhibit the diffusion of the biologically active agent.

The crystalline phase of the polymer is formed by organized and tightlypacked polymer chains. The biologically active agent dispersed in thepolymer matrix is mostly excluded from the crystalline phase.Consequently, a given amount of the biologically active agentaccumulates predominantly (in a higher concentration) in the remainingamorphous phase of the polymer matrix. Thus a depot of biologicallyactive agent can be formed from which the biologically active agent isreleased by diffusion through the amorphous phase intertwining thecrystalline domains. The flux of the agent from the system canadditionally be controlled by deposition of two or more subsequentsublayers of the polymer container layer in which the inner sublayerserves as a depot of biologically active agent (a container sublayer)and the outermost sublayer of the container layer serves as adiffusion-rate controlling barrier, also part of the container layer andmore particularly referred to as a skin layer.

In a preferred embodiment of the invention, the inner container sublayeris a semicrystalline poly(L-lactide-co-D-lactide) in which the molefraction of either of the L-lactide or D-lactide units in the copolymeris greater than about 0.7, and an outer container sublayer is anamorphous polymer such as poly(L-lactide-co-D-lactide),poly(lactide-co-p-dioxanone), or poly(lactide-co-dioxepanone), ormixtures thereof. Other preferred embodiments include an inner containersublayer having a semicrystalline polymer, or a semicrystalline mixtureof polymers, wherein the polymer or polymers are poly(L-lactide),poly(glycolide), poly(lactide-co-glycolide) or apoly(L-lactide-co-D-lactide) with the mole fraction of L-lactidestructural units in the range of 0 to 0.3 or 0.7 to 1.0, and the outercontainer sublayer is an amorphous polymer such aspoly(L-lactide-co-D-lactide), poly(lactide-co-p-dioxanone) with the molefraction of the L-lactide structural unit in the range of 0.3 to 0.7, orpoly(lactide-co-dioxepanone).

Further, other blends can be used in the container or optional barrierlayers. While polyesters like polylactide (PLA) and polycaprolactone(PCL) are rather hydrophobic polymers, exhibiting a low degree ofhydration, poly(ethylene oxide) (PEO) is a hydrophilic polymer and issoluble in water. Thus a polymer film composed of polylactide and apolylactide/poly(ethylene oxide) block copolymer can form a two-phasesystem with a hydrophobic phase, rich in PLA, and a hydrophilic phase,rich in PEO. The degree of hydration of the polymer and, consequently,the permeability of the polymer film for water and incorporatedhydrophilic biologically active agents can be increased by increasingthe fraction of the hydrophilic phase, such as PLA/PEO block copolymer,in the blend. Thus, through the variation of the PLA/PEO copolymer inthe film the release rate of certain biologically active agents can becontrolled. Similarly, depending on the degree to which a biologicallyactive agent is hydrophilic or hydrophobic, other combinations ofpolymers can be used to control the release rate of biologically activeagents.

Still further, while polylactide has a glass-transition temperature(T_(g)) in the range of 55 to 60° C., the T_(g) of poly(p-dioxanone) canbe in the range of −15° C. to −20° C. Copolymers of lactide andp-dioxanone can be made, which are crystalline and yet have a glasstransition temperature below 37° C., thus affording a pliable polymercontainer film with good permeability for incorporated compounds. Inanother embodiment of the invention, the container layer can be appliedeither in one step as a single layer or in several consecutive steps toproduce multiple sublayers. The composition in each layer or sublayer ofthe container layer can be the same or different. In a preferredembodiment, the first sublayer of the container layer to be applied iscompatible with the grafted binding layer. In following steps,additional polymer container sublayers with different compositions canbe applied on top of the first container sublayer. In this way, acontainer layer polymer film with optimized bulk (internal sublayer) andsurface (external sublayer) properties can be designed using differentpolymer compositions for bulk and surface sublayers.

It is expected that the rate of permeation of a compound, such as abiologically active agent, through the polymer layers depends on theconcentration of the compound in the polymer matrix. Accordingly, in apreferred embodiment of the invention, the bulk and surface sublayers ofthe container layer polymer film can differ in the content of thereleasably incorporated biologically active agent. Thus, the bulk layeror sublayer of the polymer with a high content of the biologicallyactive agent can be covered by a surface layer (or layers or sublayers)of a polymer with a low content of the biologically active agent. Usingthis approach, the content of the biologically active agent in the bulklayer or sublayer can be increased up to, or above, a percolationthreshold for the diffusion of the biologically active agent through thepolymer matrix, yet the release of the biologically active agent fromthe film can still be controlled by the container layer surface polymerlayer. Thus, the release rate of the biologically active agent can becontrolled by the composition and thickness of a container layer surfacelayer or layers. In a polymer matrix with more than one container layer,the outermost container sublayer may function as a skin, i.e., thislayer either does not include the biologically active agent or itsconcentration in the skin layer is significantly lower than that in theunderlying container sublayers. The skin layer can be used to furthercontrol the release of the biologically active agent. Additional skinlayers may be applied to improve the biocompatibility of the device.

The polymer layers may contain up to about 60% of the biologicallyactive agent by weight, depending on the physical properties of thebiologically active agent, such as its solubility in water, itscrystalline forms and compatibility with the polymer matrix forming thelayer. It is anticipated that a content of biologically active agentclose to the upper limit of this range can be more easily achieved withlow-solubility compounds, which at the same time exhibit a highadherence to the polymer of the container layer. On the other hand,biologically active agents with high solubility or pure miscibility withthe polymer matrix will need to be in the lower portion of this range. Atypical range of the biologically active agent content for mostapplicable compounds will be between 0 to 35% by weight. The overallweight of the coating (polymer matrix plus biologically active agent) onthe device is typically not important. The weight of the coatingattributable to the biologically active agent can be in the range ofabout 0.1 microgram to about 10,000 micrograms of biologically activeagent per cm² of the gross surface area of the device. More preferably,the weight of the coating attributable to the biologically active agentis between about 1 microgram and about 5000 micrograms of biologicallyactive agent per cm² of the gross surface area of the device. Thisquantity of biologically active agent is generally required to provideadequate activity under physiological conditions.

In turn, the coating (polymer matrix plus biologically active agent)thickness of a presently preferred composition will typically be in therange of about 0.03 micrometers to about 100 micrometers. This level ofcoating thickness is generally required to provide an adequate densityof biologically active agent to provide adequate activity underphysiological conditions.

As more fully described in the Examples, the cumulative amounts ofCVT-313 released from stainless steel plates coated bypolymer/biologically active agent composition films with differentinitial biologically active agent loadings are presented in FIG. 3. Allcurves exhibit an initial, fast release “burst” fraction, which isreleased within the first hours, i.e. almost immediately after thedevice was put into contact with the aqueous medium. This amount of“burst” originates from the fraction of the biologically active agentlocated on the polymer matrix surface, or from biologically active agentin direct contact with the polymer/medium interface and, therefore, canbe released by a convective flow. Obviously, the amount of biologicallyactive agent released in the burst fraction increases proportionally tothe initial biologically active agent loading. If it were required thatthe amount of the biologically active agent delivered in this initialphase be minimized, it would be within the scope of this invention, thatthe superficially deposited drug fraction (a “burst” fraction) can beremoved by washing as one of the steps during the manufacturing of thecoated device or before it is adjusted for implantation.

After the surface-deposited biologically active agent was washed out,the biologically active agent release becomes controlled by biologicallyactive agent dissolution and by its diffusion through the polymermatrix. The release rate increases with the increase of the initialbiologically active agent loading. For lower loadings, at levels of 10and 20%, both time dependencies of the released amount follow reasonablyclosely zero-order kinetics, with release rates almost constant for allthe period studied, i.e. up to 60 days. The slopes of the linear fits ofdata between 8 hrs and 56 days provided the release rates given in Table4 (Examples).

Still referring to FIG. 3, in the embodiment with the highest loading(25%), two phases, with faster and slower release, can be recognized andapproximated by two linear fits. While in the fast phase—lasting forabout 12 days—the release rate would be of about 1280 ng/day/cm², in thesecond, slower phase, the rate of about 380 ng/day/cm² was observed,which fits well to the predictable rate/loading dependence, based on thecomparison with lower-loading series.

These data illustrate some of the features of the present invention. Athin polymer matrix of a polymer-biologically active agent compositioncan be created on the metal surface which can efficiently control therelease of the biologically active agent through an extended period oftime. Using procedures according to the invention, thepolymer-biologically active agent matrix can be produced in areproducible way, that makes it possible to control the releaseparameters of the biologically active agent. The polymer-biologicallyactive agent polymer matrix is stable and its properties by which therelease of the biologically active agent is controlled in a predictableway are maintained for extended time periods.

Additionally, because the polymer binding layer is covalently bound tothe metal surface, the polymer matrix is resistant to cracking orpeeling. Examples 6 and 14 demonstrate the beneficial effect of thecovalent grafting of the underlining binding polymer layer to the metalsurface on the stability of the deposited polymer/biologically activeagent container layer and its resistance to cracking, fragmentation anddetachment from the surface. The superior adhesion, as a result of thecovalent binding, provides a durable polymer matrix coating for amedical device, though the device may be subjected to flexion orexpansion.

The above description defines the main features of the presentinvention. The following examples are offered, relating to thisinvention and the ways it can be carried out, in order that thoseskilled in the art may more readily understand the present invention andthe preferred embodiments thereof. These examples should not to beconstrued as specifically limiting the invention, and those variationsof the invention, which can be developed, now or later, within thepurview of one skilled in the art are considered to fall within thescope of the present invention as hereinafter claimed.

EXAMPLES Example 1 Grafting of Polylactone to Activated Metal Surfaces

Activation of the metal surface and polymer grafting. Twenty numberedsteel plates (316 stainless steel (SS)), 7×7 mm each, were successivelywashed with hexane, toluene and methanol, treated by a mixture ofsulfuric acid and hydrogen peroxide (1:1) for 1 hour at ambienttemperature, thoroughly washed by water and dried. The surface of theplates was activated by immersing the plates in a solution consisting of0.2 ml of (3-aminopropyl)triethoxysilane (“APTES”) (available, forexample, from Aldrich, Milwaukee, Wis., USA) and 20 ml of acetone andheating under reflux for four hours. Next, the plates were repeatedlywashed with acetone under nitrogen and dried in a vacuum at 60° C. Theactivated plates were transferred into a glass reactor containingcrystalline L-lactide (72 mg, 0.5 mmol) (available, for example, fromAldrich, Milwaukee, Wis., USA). The reactor content was flushed with drynitrogen in repeated nitrogen/vacuum cycles and dried under high vacuum.A solution of anhydrous dioxane (5.0 ml) containingtin(II)-ethylhexanoate (Sn(II)-octoate, 2 mg (0.005 mmol)) was addedunder inert atmosphere to dissolve the lactide and cover the plates withsolution. The solution was maintained at 80° C. for 64 hours to completethe grafting polymerization of lactide on the functional groups of the(aminopropyl)silane-activated surface SS-plates. The plates were removedfrom the polymerization mixture, washed with hot dioxane and methanol,and vacuum dried to a constant weight.

The presence and the amount of the grafted poly(lactide) layer on thesurfaces of plates was determined (a) by measuring the weight gain ofplates following the grafting polymerization, and (b) by analyzing thesurface chemical composition using ESCA (Electron Spectroscopy forChemical Analysis).

1.2. Characterization of the grafted polymer layer by measuring theweight gain of the SS plates. Using an analytical electronicmicrobalance, three values of weights for each plate were determined:W(a)—the weight of a dry plate before silane activation: W(b)—the weightof the dry silane activated plate before polymerization, and W(c)—theweight of the dry plate after polymerization. While the differencebetween W(a) and W(b) was not found statistically significant, theaverage weight gain ΔW after polymerization, determined as ΔW=W(c)−W(b),was found as 2.2±0.9 μg/plate. This corresponded to an average thicknessof the grafted poly(lactide) layer of 18 nm, assuming a uniform coverageof the surfaces.

In control experiments, matching control plates, i.e., such as platesundergoing the same polymerization reaction without being prioractivated by silane reagent, and the silane-activated plates justexposed to the lactide solution without carrying out the polymerizationreaction, did not exhibit any significant weight gain.

1.3. Characterization of the grafted binding layer by XPS analysis. Thechemical composition of the surfaces of metal plates prepared as inExample 1.1 was analyzed by ESCA using an ESCA 310 (Scienta) apparatus.Typically, the measurements were done in a vacuum of 10⁻⁹ mbar. Amonochromatic beam of AIKα (1486.6 eV) was used for electron excitation.The Auger electrons were detected at 10° and 90° angles. The elementalcomposition of the surface layer was determined from high-resolutionspectra and the integrated intensities of respective spectral lines. Thevarious chemical forms of elements found were identified based oncomparison of measured binding energies (eV) with corresponding valuesin NIST database (NIST Standard Reference Database 20, version 1.01,Bickman, D. M. and Wagner, C. D., Gaithersburg, Md. 20899, U.S.A.,1989). In ESCA, the excited electrons originate from a limited depth ofthe surface layer (of about 7 nm). This depth is dependent on theexcitation angle. Therefore, if the composition of the layer varies withthe distance from the surface, the elemental composition shown by ESCAwill vary with the excitation angle. Thus, from the angle dependence ofthe elemental composition, the information about the thickness of themodified layer can be obtained.

The characteristic data for the surface composition of plates modifiedin Example 1.1 are presented in Table 1. Atomal ratios of characteristicelements were obtained at 10° and 90° detection angles. Three series ofplates were compared: A: clean SS plates without any modification; B:silane-activated plates; C: silane-activated plates with graftedpoly(L-lactide).

TABLE 1 % A B C Element 10° 90° 10° 90° 10° 90° Cr 22.0 23.5 5.1 12.00.1 1.3 Ni 2.0 1.3 0.2 1.2 0 0 Fe 8.6 6.0 1.7 3.8 0 0 Si 0 0 7.3 4.6 2.83.0 N 0 0 7.5 3.4 0.6 0.6 C 15.7 17.7 28.2 32.4 44.4 25.4

The first group of elements (Cr, Ni, Fe) is characteristic for thecomposition of the bare metal surface (316 stainless steel). Some carbon(and oxygen) is regularly present on the surfaces of untreated metal asan impurity. Si and N (in addition to carbon) are characteristicelements of the siloxane activating layer as follows from their presenceat surfaces of series B and C. The decreased content of Cr and othermetals at the surfaces of series B and C confirms the modification ofthe surface by silane activation and, in particular, coverage of themetal by grafting of lactide. In series B, the higher content of Si forlow incident angle (10°) indicates that the most superficial layer isricher in Si with respect to the deeper layers, which correspondinglyshow higher content of Cr and other metals. Practically completedisappearance of electrons originating from Cr and other metal elementsin series C, confirms a complete coverage of the metal by the graftedpolymer, and makes it possible to estimate a minimum thickness ofgrafted PLLA layer as being higher than about 10 nm, which correspondswith the thickness of the grafted layer estimated by weighing (Example1.2). The presence of a significant layer of PLA is also confirmed bythe increased content of carbon and its angle dependence.

The analysis of the binding energy of emitted electrons provides theinformation about the chemical forms in which the elements are presentin the surface layer, thus makes it possible to confirm the anticipatedchemical processes. The characteristic data showing the changes in thecomposition of characteristic chemical groupings after grafting oflactide to the silane-activated metal surface as in Example 1.1 arepresented in Table 2. B: silane-activated plates (APTES); C:silane-activated plates with grafted poly(L-lactide).

TABLE 2 Chemical form % Element (binding energy, eV) B C C CH_(x) (284.5eV) 33.3 29.2 C—O (286.1 eV) 6.9 10.3 C═O (288.0 eV) 4.5 6.0 O C═O(531.3 eV) 21.4 37.3 N —NH₂ (399.5 eV) 3.7 0 —NH— (400.4 eV) 0 2.7

The covalent grafting involving the acylation of functional groupspresent in the (aminopropyl)silane-activated layer is confirmed by thechanges of characteristic chemical structures. At the(aminopropyl)silane-activated surfaces nitrogen (N, 1 s) is present in aform of amine. After grafting with lactide, the acylation of the aminegroups and formation of amide is confirmed by the change of bindingenergy of nitrogen electrons to that characteristic for amide.Correspondingly, the formation of the polyester structure is indicatedby the increase in the content of carbonyl groups.

The presence of initiating amine groups on the silane-activated surfacewas also documented by analyzing the mole amount of amine groups on theactivated surface as follows. The plates were immersed in a 0.1%solution of 2,4,6-trinitrobenzenesulfonic acid in 3% borate buffer (pH8.15) for 5 minutes at 70° C. Then, the plates were thoroughly rinsedwith water to remove the unbound reactants and treated with a solutionof NaOH (1 mol/L) at 70° C. for 10 minutes. The amount of liberatedpicric acid was determined by reverse phase HPLC chromatography. Thecontent of amino groups determined by this procedure on differentbatches of activated SS plates prepared by the procedure described inthis Example was typically in the range of 0.4 to 1.5 nmol/cm².

1.4. Deposition of the container polymer layer. To evaluate the effectof the grafting (or binding) layer on the properties of polymer coatingcomposition, controlled experiments with well-defined coating procedureswere performed. Additional layers of polymers were deposited on thepolymer-grafted plates by using a spin-coating process. In general, asolution of the polymer in a solvent was applied on one surface of theplate and spread over it by spinning the plate in the spin-coatingapparatus (Headway Instruments). After evaporation of the solvent andvacuum drying, the amount of deposited polymer was determined byweighing. The surface profile of the polymer layer was analyzed by meansof a surface profiler (Surface Profiler Tencor, model AlfaStep 500). Thethickness of the deposited polymer (or container) layer could be wellcontrolled by the concentration of the applied polymer solution and bythe frequency of spinning. Additionally, several subsequent layers ofthe polymer could be deposited on the top of previous one by applyingthe same procedure. This procedure made it possible to form well-definedpolymer layers in a reproducible way on grafted and non-grafted plates.

Poly(L-lactide) (PLLA, M_(w)=365 000) was deposited using the abovedescribed procedure as a solution in dioxan (2% w/w) on the surfaces ofthree series of SS plates (n=5 each) prepared as in Example 1.1: seriesD: clean SS plates without any modification; series E: silane-activatedplates without further modification; series F: silane-activated plateswith grafted poly(L-lactide). Four successive layers of poly(L-lactide)were deposited in each series. The average deposited amounts andthickness of the polymer layer are shown in Table 3.

TABLE 3 Layer Thickness Series 1^(st) 2^(nd) 3^(rd) 4^(th) Total (μg)(μm) D 34.4 ± 2.3    64.4 ± 97.2 ± 5.3 105.6 ± 5.4 301.6 ± 5.03 ± 0.11 3.4  6.8 E 42.2 ± 2.7    70.8 ± 92.8 ± 4.1 103.2 ± 5.2 309.0 ± 5.15 ±0.08  3.1  4.8 F 55.8 ± 4.2  75 ± 105.8 ± 14.6 109.6 ± 6.7 346.2 ± 5.77± 0.21  3.9 12.7  

The data in Table 3 show that the thickness of the newly depositedpolymer layer depends on the properties of the underlying surface. Theincrease in the amount of the polymer deposited in the second and thirdlayers reflects the improved adhesion of the polymer to the underlyingsurface because the deposition is done on the layer of the same polymerdeposited previously. In addition, when the second and any subsequentlayers are deposited, the solvent of the applied solution partlypenetrates into the underlying polymer, leaving the spreading solutionmore viscous, thus increasing the thickness of the spread layer. Whilethe differences in these effects become negligible for third and anysubsequent layers, the differences between series D, E and F in theamount deposited in the first layer reflect their differences in thesurface properties. The significantly higher amount of the polymerdeposited in the series F, compared to series D and E, reflects thehigher adhesion of the deposited polymer to the underlying covalentlygrafted polymer binding layer as well as solvent penetration into it.

The deposited polymer layer (or container layer) can be dissolved in asuitable solvent and completely washed down from the plates. In theabove described experiment, the series of plates containing thedeposited PLLA layers were thoroughly washed with chloroform, which is agood solvent for PLLA. In the series F plates, the covalently graftedpolylactide layer remained on the surface of the plate even afterextensive washing of the deposited PLLA layer (a container layer), andits persistent presence on the metal surface was proved by both the XPSanalysis and surface-profile methods as described above. In the series Eand D, the washing of deposited PLLA (a container layer) caused acomplete removal of deposited PLLA and their surface characteristics, asdetermined by the above methods, indicated a silanized and baremetal-oxide surfaces in the series (E) and (D), respectively.

These experiments show that the grafting procedure according to thisinvention produces a covalently bonded polymer layer (a binding layer)on the metal surface. The binding layer is resistant to removal bydissolution in a good solvent for the polymer. The covalently graftedbinding layer improves the adhesion of the adjacent layer (layers) of acompatible polymer, deposited on top of it (as the container layer).

Example 2 Surface Activation with APTES in Vapor Phase

SS plates, similar to those in Example 1.1, were rinsed with toluene,methanol and distilled water, blown dry with stream of nitrogen andplaced in a vacuum chamber of a radio frequency glow discharge (RFGD)plasma generator (Model 220RGD-200, REFLEX Analytical Corp. Ridgewood,N.J.). Plates were treated with argon plasma for 3 to 5 min (80 to 100W, 1 to 10 mbar). Surfaces prepared with this procedure showed noorganic contamination by ESCA analysis. The freshly plasma-cleanedplates were placed in a glass container, where they were fixed in a PTFEholder which kept their flat surfaces facing the liquid at the bottom ofthe container. The container was flushed with nitrogen saturated withwater vapors and 0.5 ml of APTES was dropped at the bottom under thenitrogen shield. The plates were exposed to APTES vapors for intervalsof from 10 minutes to 16 hours. After exposure to silane vapors theplates were removed from the container, purged with nitrogen, evacuatedand heated in a vacuum oven to 60° C. for 2 hours to remove residualphysically adsorbed silane reactant.

The amine functional groups on the activated surface were determined asfollows. The plates were immersed in a solution of2,4,6-tri-nitrobenzenesulphonic acid in 3% borate buffer (pH 8.15) for 5minutes at 70° C. Then, the plates were thoroughly rinsed with water toremove the unbound reactants and treated with a solution of NaOH (1molL⁻¹) at 70° C. for 10 minutes. The amount of liberated picric acidwas determined by a reversed phase HPLC chromatography. The content ofamino groups was found to be 0.6, 0.9 and 1.2 nmol/cm², for platestreated with SAR for 10, 30 and 60 min, respectively. The content ofamine groups on the surface reached saturation after 60 minutes ofexposure.

The activated plates were grafted by in situ polymerization of L-lactidein dioxane by the procedure described in Example 1.1. The graftingefficiency, estimated from the ESCA analysis and the thickness of thegrafted layer was essentially the same as that described in Example 1.1.

Example 3 Bis-N-(2-hydroxyethyl)aminopropyl triethoxysilane as a SilaneActivating Reagent

Bis-N-(2-hydroxyethyl)aminopropyl triethoxysilane was used instead ofAPTES as a silane activating reagent (SAR) in a manner described inExample 1.1. By carrying out the grafting polymerization according toExample 1, metal surfaces containing an average amount of 2.6±0.8 ug/cm²of covalently bound polylactide were obtained. The plates were furtherused for deposition of the container polymer layer as it was describedin Example 1.4.

Example 4 Grafting of poly(D,L-lactide) to APTES Activated Metal Surface

10 pieces of SS plates analogous to those described in Example 1, wereactivated by the reaction with APTES as in Example 1, to provide metalsurfaces with the average content of amine groups 0.8 nmol/cm². Theactivated plates were placed in a glass ampule and 2.9 grams ofcrystalline D,L-lactide (m.p. 125° C.) and 40 mg of tin(II) octanoatewere added. The ampule was flushed by dry nitrogen using repeatedvacuum/nitrogen cycles, kept at 60° C. under a high vacuum for 2 hoursand sealed under vacuum. The sealed ampule was heated in an oil bath to180° C. in order to melt the lactone. While taking care that all plateswere immersed in the lactone melt, the reaction was kept at 180° C. for24 hours. During this period, the lactone melt became viscous. Whentaken our of the heated bath, the lactone melt solidified to a glassysolid. The solid polymer was dissolved in chloroform, the plates wereremoved and repeatedly washed with hot dichloroethane and dried instream of nitrogen and vacuum. The presence of poly(D,L-lactide) (PDLLA)grafted to the metal, i.e. the polymer remaining on the surface afterthorough washing with the solvent, was confirmed by the methodsdescribed Example 1. The average thickness of the grafted polylactidelayer was estimated to be about 20 nm. The PDLLA-grafted plates weresuitable for deposition of a polymer coating layer (container layer) ina similar way as it was described in Example 1.

Example 5 Release of Biologically Active Agent from Coated Metal Surface

SS plates (7.1×7.1 mm, surface area ˜50 mm²) analogous to thosedescribed in Example 1, were activated by the reaction with APTES andgrafted by polymerization of lactide, as in Example 1.1, to provide aPLA binding layer on the metal surfaces with an average content ofgrafted PLA of 3.5 micrograms/cm².

Additional PLA layers (container layers) containing a biologicallyactive agent were applied to the grafted plates. Thepolymer-biologically active agent layers were cast on one side of eachSS-plate by applying a dioxane solution of PLA and the biologicallyactive agent and spreading it on the surface of the plate by spinning itin a spin-coater device (Headway Instruments). The solvent wasevaporated from the spread layer of the polymer solution to solidify thepolymer film (as a container layer). Another layer of thepolymer-biologically active agent composition was applied in the sameway (to form another sublayer of the container layer), when the previousone was fully dried. The average thickness of the container layer wasdetermined by weighing. The actual average biologically active agentloading for any given sequence of polymer-biologically active agent filmdeposition was determined by dissolution of films from a control seriesof plates and measuring the biologically active agent content in therecovered solution.

The PLA polymer used was poly(D,L-lactide), (PDLLA, MW=800,000) and itsconcentration in the dioxane solution was 18 mg/ml. The biologicallyactive agent, CVT313, is a purine derivative, which has been shown as aCDK2 inhibitor (Brooks, E. E., et al., J. Biol. Chem 1997, 272, 29207).

Three series, G, H and J, of coated plates were prepared by applying thesolutions containing the same concentration of PDLLA and thebiologically active agent in the concentration of 2, 4, and 6 mg/ml,respectively. The PDLLA-CVT313 container layers were produced byapplying two subsequent sublayers for each plate, thus providing forcoatings with an average thickness of 2.9 micrometers and with averagecontents of CVT313 in the polymer matrix of series G, H and J being10.3, 18.9 and 25.1% (w/w), respectively.

The one-side-coated SS-plates were suspended in a buffered salinesolution of pH 7.4 in a stoppered spectrophotometer cell with the coatedsurface exposed to the solution. The cell was placed in a metal holderallowing the buffer to be stirred in a constant rate by means of amagnetic stirrer and to keep the temperature constant at 37° C. Theincubation of the plates carrying the polymer-biologically active agentpolymer matrix was carried out for two months. In this time period, theconcentration of the biologically active agent released to the bufferwas determined by measurement of UV-absorption spectra of the solution.The amount of released biologically active agent was determined from thebiologically active agent concentration and the volume of the recipientsolution and plotted against time of incubation. The daily release ratewas calculated from linear portions of the release profiles. Thecumulative amounts of CVT313 released from the three series of platescoated by polymer-biologically active agent polymer matrix films withdifferent initial biologically active agent loadings are presented inFIG. 3. The average values of triplicate release data are plottedagainst linear time scale.

After 60 days, the plates were removed from the buffer, rinsed by waterand dried under vacuum. The content of the residual agent in the polymercoating was determined by dissolution of the coating in chloroform andmeasuring the content of the agent in the solution by HPLC. A summary ofthe quantitative data is given in Table 4.

TABLE 4 Parameters of the release system (units) G H J Film thickness(μm) 2.88 2.85    3.02 Initial loading of the biologically active 10.318.9   25.1 agent in the matrix (%) Fraction released during 60 days (%)46 41 40 Fraction remaining in the matrix (%) 53 56 57 Initial-burstfraction (%) 5.4 8.6   10.5 Release rate^((a)) (ng/day/cm²) 200 3201280^((b) )  380^((c)) ^((a))extrapolated from the linear fit of thereleased amount vs. time dependences; ^((b))based on the initialfast-release phase (see FIG. 3); ^((c))based on the second slow-releasephase (see FIG. 3).

Example 6 The Effect of Coating Stability on the Release of BiologicallyActive Agent

Three series of SS-plates (n=6, each), analogous to those of Example 1,were prepared. Series K consisted of plates activated by the reactionwith APTES and subsequently grafted by in situ polymerization ofpoly(D,L-lactide), using the procedure described in Example 1. Series Lconsisted of plates activated by reaction with APTES as asilane-activating agent only. The series M was composed of bare cleanedSS-plates without further modification.

A container layer of the same PDLLA/CVT313 polymer/biologically activeagent solution was deposited by spin casting from a dioxane solution onone side of plates of all three series K, L, and M, using the proceduredescribed in Example 5. The average thickness of the deposited coatingswas 3.1±0.2 micrometers, and the average content of CVT313 in thedeposited container layer was 11.4±0.3% (w/w) for all three series. Theplates were individually immersed in a phosphate buffered salinesolution (PBS, pH 7.4) and the release of the biologically active agentfrom each plate was followed as described in Example 5.

In series K (polymer/biologically active agent solution deposited on PLAgrafted surface), release profiles closely corresponding to those shownfor series H of Example 5 were observed for all plates in the series(n=6). The average release rate in the period between 1^(st) and 12^(th)days was found to be 208±12 ng/day/cm². The average fraction of thebiologically active agent remaining in the polymer matrix after 12 daysof the release experiment was 78±6% of the original loading. Inspectionof the container layer under the optical microscope showed unperturbeduniform polymer matrix over all of the plate surface.

In series L (polymer/biologically active agent composition deposited onSS modified by silane activation only), the release profiles showed arapid increase in the release rate starting from the second day of therelease experiment in some plates. Within four days, the fraction of thebiologically active agent released to the medium approached 100% for allplates in the series. The inspection of the container layer under themicroscope showed a progressive cracking of the container layer startingon the second day of the experiment, followed by peeling of fragments ofthe polymer film from the surface.

In series M (polymer/biologically active agent composition depositeddirectly on the bare metal surface), the release profiles were analogousto those of series L. The disturbances in the release rate due tofragmentation of the container layer and its peeling from the metalsurface started within 24 hours after the plates were immersed in PBS.The visual inspection under microscope confirmed insufficient adhesionof the deposited polymer/biologically active agent film to the surface.

Example 7 Release of Biologically Active Agent from Coating with PDLLASkin

Two series of SS-plates, N and P, were treated by silane activationreagent and grafted by in situ polymerization of lactide, applying theprocedures described in Example 1. In both series, one side of theplates with a surface area of 50 mm² was coated (container layer formed)by polymer/biologically active agent composition composed ofpoly(L-lactide) (PLLA) and CVT313, which was applied in two sublayers asa solution in chloroform using the spin-coating method. The average filmthickness PLLA/CVT313 composition was 2.74±0.16 micrometers and theaverage content of CVT313 in the film was 28.8±1.2% (w/w). In series N(n=4), an additional coating layer of pure PDLLA (a “skin”, void of theagent) was applied on the top of the PLLA/CVT313 film. The plates ofseries P (n=4) were used without any additional modification.

The plates of both series were immersed in a stirred PBS solution andthe release of biologically active agent to the solution was monitored.The time profiles of the release of CVT313 from PLLA matrix and PLAAmatrix with PDLLA “skin” are shown in FIG. 4. The release parameters ofboth systems are summarized in Table 5.

TABLE 5 N Parameters of the release system^(a)) (PLAA + PDLLA P (units)skin) (PLLA) Film thickness (μm) 3.06^(b)) 2.74 Initial loading of thebiologically active 24.6^(c)) 28.8 agent in the matrix (%) Fractionreleased during 12 days (%) 42.5 93.4 Fraction remaining in the matrix(%) 62.4 13.4 Initial-burst fraction (%) 15.2 20.6 Release rate(ng/day/cm²) 2040 8300 ^(a))average values, n = 4 ^(b))composed of 2.74μm of PLLA/CVT313 matrix and 0.32 μm PDLLA skin ^(c))including the skinlayer in the calculation

Example 8 Release of Biologically Active Agent from Coating of BoneFixation Plates

Bone-fixation plates (stainless steel, 7×49 mm) were activated by thereaction with APTES and subsequently grafted by in situ polymerizationof D,L-lactide according to Example 4.

The grafted plates were coated by a poly(D,L-lactide)/dexamethasonecomposition by a dip-coating procedure as follows. The plate, hung on awire holder through a hole in the plate, was immersed in a solution ofPDLLA and dexamethasone in chloroform for about 10-15 seconds, andremoved from the solution in a vertical position. The excess of thesolution collected at the bottom end of the plate was dried by touchingwith paper tissue. The plate wetted by the composite solution was thenplaced flat on a support holding it in a horizontal position and dried.The drying took place at room temperature under a stream of nitrogen (2hours), followed by drying in a vacuum oven at 50° C. (16 hours). Byevaporation of the solvent, a contiguous layer of polymer/biologicallyactive agent film was formed. The amount of depositedpolymer/biologically active agent composition was determined byweighing.

Using the above procedure, two series of plates were prepared. Thepolymer used was poly(D,L-lactide) (PDLLA, MW=800 000). The agent wasdexamethasone (Sigma, Cat. No.: D1756). The composition ofPDLLA/dexamethasone solutions in chloroform used for dip coating was:series A (n=3): PDLLA, 17.05 mg/ml, dexamethasone 4.15 mg/ml; series B(n=3): PDLLA, 18.05 mg/ml, dexamethasone, 2.64 mg/ml. The averagethickness of the film in both series was about 1.6 μm (estimated fromthe weight of the coating and the surface area of the plates). Based onthe composition of the coating solution, the initial biologically activeagent loading was 19.6% w/w and 12.8% w/w for the series A and B,respectively.

The release of dexamethasone from plates in a simulated body fluid(buffered isotonic saline solution with bovine serum albumin) wasfollowed at 37° C. for 12 days. The amount of released dexamethasone wasdetermined by HPLC in the samples withdrawn from the incubation solutionat selected time intervals. The obtained release profiles, expressed asa cumulative fraction of biologically active agent released with time,are given in FIG. 5.

The data in FIG. 5 demonstrate that the polymer coating composition wasprovided with the capacity to control the release of incorporatedanti-inflammatory drug, dexamethasone, for an extended time period andto deliver the drug in a predictable fashion to the surroundingenvironment, such as simulated body fluid. The release rate and,therefore, the daily delivered dose, of the drug was dependent on thedrug loading in the composition.

Example 9 Release of Biologically Active Agent from Coated CoronaryStents

A series (n=5) of balloon expandable coronary stents (stainless steel,3×16 mm) (Pulse Corporation) may be surface activated (to form anactivating layer) and grafted (to form a binding layer) by the in situpolymerization of D,L-lactide using the procedure described in Example2. The grafted stents may be coated by a composition consisting of 78%of poly(lactide-co-glycolide) copolymer (lactide/glycolide ratio: 15/85)and 22% of warfarin sodium (an anticoagulant drug, MW 330) (to form acontainer layer), by applying the mixture of both components as asolution in hexafluoropropanol (HFP) by dipping the stent in thesolution. The polymer/biologically active agent film should besolidified by evaporating the solvent in vacuum. After complete removalof HFP, an additional coating layer (a barrier or skin layer) ofpoly(D,L-lactide) can be applied from the solution of PDLLA in acetoneas described in Example 7.

The release of warfarin from the coated stents in simulated blood plasma(buffered isotonic saline solution with bovine serum albumin) can befollowed as described in Examples 5 through 8. The amount of releasedwarfarin may be determined by a reverse-phase HPLC in 24 hoursintervals. Based on the analysis of the release profiles, the coatedcoronary stents thus produced should provide for a sustained release ofthe anticoagulant agent in the dose of 0.85 μg/day/stent for the periodof more than 8 days, which dose could be administered locally to theimplantation site. The release of anticoagulant agent thus can improvethe performance of the stent after its implantation.

Example 10 Release of Biologically Active Agent from Coated MandibularImplant

A titanium mandibular implant may be treated by oxygen RFGD plasma andsubsequently surface activated by the reaction withbis-N-(2-hydroxyethyl)aminopropyl triethoxysilane in a vapor phase (toform the activating layer). The activated surface may be grafted (toform the binding layer) by the in situ polymerization of ε-caprolactonein THF, with tin(II)-ethylhexanoate as a catalyst. The thickness of theresulting grafted (binding) layer can be determined by means of asurface profiler (Tencor, model AlfaStep 500) and is expected to be inthe range of 10 to 30 nm. The grafted implant can be coated (to form acontainer layer) by a composition, consisting of 74% ofpoly(caprolactone) (MW 80000) and 26% of mitomycin, as a solution inchloroform, by spraying the solution on the implant in layers. Eachsprayed sublayer of solution should be dried in a stream of hot nitrogenbefore another layer is applied. The top most layer (barrier or skinlayer) may be applied from a solution of poly(caprolactone) only,without the biologically active agent. The average thickness of thecomposite coating (polymer matrix plug biologically active agent) on theimplant surface is expected to be in the range of 15 to 20 μm. Thus, amedical implant, releasing a dose of 180 μg/day/cm² of anantiproliferative and antimicrobial agent in a sustained way, can beproduced.

Example 11 The Release of CVT313 from Coated Coronary Stents

A series (n=3) of balloon expandable coronary stents (stainless steel,16 mm) (Pulse Corporation) were surface activated by the reaction withAPTES and grafted (binding layer) by the in situ polymerization ofL-lactide using the procedure described in Example 1. The grafted stentswere coated (container layer) by a composition consisting ofpoly(D,L-lactide) (PDLLA, Mw=625,000) and a biologically active agent.The agent, CVT313, is a purine derivative, which has been shown as aCDK2 inhibitor (Brooks, E. E., et al., J. Biol. Chem 1997, 272, 29207).

The coating (container layer) of stents was accomplished by spraying asolution of PDLLA (56.0 mg) and CVT313 (4.35 mg) in dioxane (8.60 ml) onthe spinning stent, using a microspray device with nitrogen as a carriergas. The solvent was left to evaporate at room temperature and finallydried under vacuum. A uniform, contiguous, and smooth coating(container) layer on all surfaces of the stent struts was obtained withaverage thickness of about 1.1 μm. The average total weight of thecoating layer on the stent was 65.9±2.2 μg and the average content ofthe active agent in the coating composition (container layer) was 7.2%w/w.

The release of CVT313 from the coated stents in phosphate bufferedisotonic saline was followed under constant stirring rate of thesolution at 37° C., for 35 days. The amount of released agent (CVT313)was determined by HPLC. Based on the analysis of the release profiles,the coated coronary stents thus produced provided for a sustainedrelease of CDK2 inhibitor for a period of more than 35 days. During theperiod between day 1 and day 35, the release profile was almost linearwith an average dose of released CVT313 being 72 ng/day/stent. Duringthis period about 51% of the incorporated agent was released. Theanalysis of the residual amount in the coating matrix gave 48% of theoriginal amount of agent still residing intact in the coating matrix.Taking into account the residual amount of agent and the average rate ofrelease on day 35, when the experiment was terminated, one canextrapolate the capacity of the device to release the agent for a totalof about 70 days. The release profile and the variation in the releaserate between individual stents in the series is shown in FIGS. 6 and 7.

Example 12 The Release of Bioactive Agent from Semicrystalline andAmorphous Matrices

SS plates (7.1×7.1 mm, surface area ˜50 mm2) analogous to thosedescribed in Example 1, were activated by the reaction with APTES andgrafted by polymerization of lactide, as in Example 1.1. A PLA polymercontainer layer containing a biologically active agent was applied ontothe grafted lactide layer by spin casting from a polymer-agent solution.

The polymers used for the container layers were

poly(D,L-lactide), (PDLLA, MW=800,000),

poly(L-lactide), (PLLA, MW=365 000) and

a copolymer of L-lactide and D,L-lactide,poly(L-lactide-co-D,L-lactide), prepared from L-lactide and D,L-lactidemonomers in the ratio of 1:1, (P-LL-co-DL, MW=350 000),L-lactide/D-lactide structural units ration in the copolymer=0.75)

Five series of SS plates, designated as series Q, R, S, T, and U, coatedby the above polymers as follows. In series Q the polymer of containerlayer was PLLA; in series R the container layer was cast from themixture of PLLA and PDLLA in the ratio of 3:1 (w/w); in series S thecontainer layer was composed of a PLLA and PDLLA mixture in the ratio of1:1; in series T the container layer was cast from the solution ofcopolymer P-LL-co-DL (1:1); and in series U the container layer wascomposed of PDLLA. Consequently, the approximate composition of polymerforming the container layer in series Q, R, S, T, and U with respect tothe ratio of L-lactide and D-lactide structural units was expected to beas follows:

Series L-Lactide/D-lactide ratio Q 1.00 R 0.88 S 0.75 T 0.75 U 0.50

In all series the container layer was cast from the solution of polymer,or mixture of polymers, and the agent in dioxane. The concentration ofpolymers in the dioxane solutions was 16 mg/ml.

The agent used in all series was CVT313, a purine derivative, known as aCDK2 inhibitor (Brooks, E. E., et al., J Biol. Chem 1997, 272, 29207).The average content of the agent in the container layer was the same forall series and was equal to 172±7 ug/mg of polymer-agent composition,i.e. the loading degree of 17% (w/w).

The one-side-coated SS-plates were suspended in a buffered salinesolution of pH 7.4 in a stoppered spectrophotometer cell with the coatedsurface exposed to the solution and the amounts of the agent releasedfrom the coatings were determined by measurement of UV-absorptionspectra of the solution. The amount of released agent was determinedfrom the agent concentration and the volume of the recipient solutionand plotted against time of incubation. The cumulative fractions ofCVT313 released from the five series of plates coated by polymer-agentcomposition films with same content of the agent and different ratio ofL-lactide and D-lactide structural units in the polymer matrix arepresented in FIG. 8. The average values of triplicate release data areplotted against a linear time scale.

The release data for the series of polylactide compositions withdifferent ratio of d-lactide and L-lactide structural units in thematrix demonstrate that the release profile, i.e. the release rate andthe fraction released in the fast initial phase, depends on theenantiomer composition of the polylactide matrix. All five series of SSplates contained the same initial amount of the agent (loading of about17%). While the series with highest content of L-lactide (series S, purePLLA) exhibits the highest amount of drug released within the initialfast-release phase, with increasing content of D-lactide in the polymercomposition (series R, S, T, with L-Lactide/D-Lactide ratio ranging from0.9 to 0.7) the release profile gradually changes, showing lowerfast-releasing fraction and better diffusion-controlled release. Forcompositions with about 30% of D-lactide units in the polymer, therelease profile approaches that of series U, i.e., PDLLA(L-lactide/D-lactide=0.50). These data indicate, that for the ratios ofL-LA/D-LA below 0.7 (i.e, for the content of D-lactide units inpolylactide above 30%), the fraction of amorphous regions becomesdominant, and the exclusion of the drug from the crystalline regionsdoes not significantly affect the distribution of the agent within thematrix. It is also worth noticing, that the release rates in the second(slow) phase of release are similar for all series, what is in accordwith the prevalence of diffusion of agent molecules through theamorphous parts of the matrix, hence, that part of the matrix which hassimilar character in all five series.

The example demonstrates the mechanisms by which the ratio ofcrystalline and amorphous phases in polylactide blends and copolymersaffects the release profile of the incorporated agent. It alsodemonstrates the range in the ratio of D/L enantiomers which iseffective in modulation of the release rate through the ratio ofcrystalline/amorphous phases, indicating that compositions, eitherblends or copolymers, with L/D ratio below 0.7 (or, alternatively, above0.3) behave as predominantly amorphous.

Example 13 Biological Effect of the Agent Released from the PolymerCoating

Series of SS plates (7.1×7.1 mm, surface area ˜50 mm2) analogous tothose described in Example 1, were activated by the reaction with APTES,grafted by polymerization of D,L-lactide by the procedure described inExample 1.1., and polymer-agent compositions consisting of either PDLLAor PLLA matrix with different loading of CVT313 were cast on one side ofthe SS plates. The plates were pre-incubated with PBS (phosphatebuffered isotonic saline) for 17 hours to remove a fast releasing(burst) fraction of the incorporated drug, rinsed by the buffer andsterilized by exposure to UV light. A group of 3 plates was randomlyselected from each series and used for determination of the releaserate. The remaining plates in the series were used for tissue-cultureexperiments. Thus, series of plates V, W, X, and Y, releasing differentdaily doses of CVT313 into incubation medium in a constant, zero-orderrate were prepared. The parameters of the series are displayed in Table6. The release rate numbers given in Table 6 are doses delivered to eachculture cell. The release rate numbers in parentheses are the numbers ona per cm2 basis.

TABLE 6 Characteristics of sustained-release coatings on the series ofSS-plates Series Parameter V W X Y Number of plates in the 18 18 18 10experiment Polymer matrix PDLLA PDLLA PDLLA PLLA Container layerthickness (um) 2.0 1.8 1.4 1.2 CVT313 loading (% w/w) 3.7 7.5 23 18Release rate (dose) (ng/day) 27 (54) 82 (164) 222 339 (444) (678)

The sterile plates were placed in the wells of a tissue-culture plate,which already contained pre-cultivated and well-adapted cells adhered tothe bottom. 24-well culture plates were used with the cultivationsurface of 2.0 cm²/well, and the volume of the medium was 2.5 ml/well.3T3 mouse fibroblasts were used as testing cell culture. 5000-10000cells were seeded per well. At 24 hour intervals the culture medium wasremoved by aspiration and replaced by the same volume of the fresh one.

At given times, the designed plates, containing the treated wells withdrug-loaded coupons, the wells with the control coupons and the controlwells without any treatment were processed for MTT test. Triplicatewells were used for treated and control series for each time interval.

MTT test: The culture medium was removed and the MTT solution(3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide) in PBS(600 ul/well) was added to each well. The plates were incubated for 2 hin 37° C. The blue formazan stain formed was dissolved in iso-propanoland the optical density was measured using an automatic microplatereader. If needed, in cases of high contents of cells, the measuredsolution was appropriately diluted by iso-propanol for optical densityreadings. The relative cell proliferation, as a result of the inhibitoryeffect of the released drug, was determined as the ratio of the meanoptical density of treated wells with respect to that of the controls.

The effect of sustained release of CVT-313 on the growth of 3T3 cellswas expressed in terms of relative proliferation, i.e. as a ratio ofquantity of cells grown under the influence of CVT-313 and that of thecontrol (undisturbed culture). The values for the second control (theculture exposed to coupons coated with the polymer only, without thedrug) are presented for a comparison. Table 7 shows the relativeproliferation rates of mouse 3T3 fibroblasts exposed to CVT313 releasedfrom polymer coatings and to sham controls (SS plates coated by thepolymer only, void of agent). n—not determined, because of completeinhibition of the cell growth.

TABLE 7 Series V W X Y Dose 27 ng/day 82 ng/day 222 ng/day 339 ng/dayreleased CVT313 control CVT313 control CVT313 control CVT313 control day3 1.00 1.03 0.88 1.03 0.42 0.98 0.30 0.98 day 6 0.94 0.99 0.69 1.00 0.141.06 0.03 0.97 day 9 0.93 1.04 0.64 1.04 n n n n

The experiment shows that the CVT313, a CDK2 inhibitor, can be releasedfrom polymer coatings under this invention in a sustained releasemanner. The extend of inhibition effect can be controlled by thereleased dose, which in turn is dependent on the parameters of thecoating as shown in this and previous examples.

Example 14 Stability of Stents Containing Biologically Active Agent

Series (n=10) of balloon expandable coronary stents (stainless steel,length: 16 mm, diameter in compressed state: 1.6 mm, Pulse Corporation)were surface activated by the reaction with APTES. Then the series wasdivided in two groups (n=5). Group A was grafted by the in situpolymerization of D,L-lactide using the procedure described inExample 1. Group B was left without grafting. Both groups of stents werecoated by a composition consisting of poly(D,L-lactide), (PDLLA, Mw=625000) and a biologically active agent, CVT313.

The coating of stents was accomplished by dipping the stent in asolution of PDLLA (44.0 mg) and CVT313 (3.57 mg) in dioxane (8.00 ml).The solvent was left to evaporate at room temperature and finally driedunder vacuum. The average thickness of the coating layer was determinedfrom the weight of coating and the surface area of the stents, takingthe value of 1.22 g/cm3 as the density of the coating layer. Averagethickness thus determined was about 0.9 um. The average content of theactive agent in the coating composition was 7.5% w/w.

The quality, uniformity and surface smoothness was examined by using ascanning electron microscope, SEM, (Jeol 200A). Both groups of stentsexhibited a uniform, contiguous, and smooth coating layer on allsurfaces of the stent struts.

Stents were than individually placed on the balloon of a ballooncatheter for angioplasty and expanded to a diameter of 3.5-3.6 mm. Theexpanded stents were examined again by SEM. Observations of stents fromgroup A (containing a grafted layer of the in situ polymerizedD,L-lactide) and group B (without a grafted layer) were compared.

In some stents of the group B, the expansion of the stent producedcracks in the coating layer, which were typically located in the regionof the highest stress due to stent deformation, such as inner surfacesof some strut loops.

On the other hand, all stents of group A (modified by polymerizationgrafting) exhibited a smooth and contiguous coating layer after theexpansion. Neither cracks nor any signs of peeling the coating polymerlayer were found.

This observation confirmed the beneficial effect of the binding polymerlayer (obtained by grafting polymerization) on the stability of thecoating layer and on its resistance to mechanical stress, that can beproduce during use of some medical devices, such as coronary stents. Thedescribed experiment thus demonstrates the advantageous features of thecoating procedure according to the invention.

Example 15 Surface Properties of the Polymer Coatings

Glass slides (20×20×0.18 mm) (n=20) were thoroughly washed by ethanoland water and dried under stream of air (Group A).

A group of slides A was separated (n=16) and their surfaces wereactivated by the reaction with the solution of3(N,N-bis-hydroxyethylamino)propyl-triethoxysilane in acetone (1%). Theglass slides were rinsed by acetone and dried in vacuum. (Group B)

A group of surface-activated glass slides of B was separated (n=12),they were placed in a reactor containing crystalline L-lactide (144 mg,1.0 mmol) (Fluka GmbH, Switzerland). The reactor content was flushedwith dry nitrogen in repeated nitrogen/vacuum cycles and dried underhigh vacuum. A solution of anhydrous toluene (20.0 ml) containingtin(II)-ethylhexanoate (Sn(II)-octoate, 4 mg (0.01 mmol)) was addedunder inert atmosphere to dissolve the lactide and cover the plates withsolution. The solution was maintained at 80° C. for 64 hours to completethe grafting polymerization of lactide on the hydroxyethyl functionalgroups of the silane-activated glass surface. The slides were removedfrom the polymerization mixture, washed with hot toluene and methanol,and vacuum dried. (Group C)

A series of PLLA grafted glass slides (n=8) was selected from the groupC. A PLLA layer was deposited on one side of each slide by spin castinga solution of PLLA (MW=365 000) in chloroform (0.8 mg/ml) andevaporating the solvent to dryness. The same procedure was applied tocoat the other side of each slide. In this way we have prepared glassslides coated on both sides by a homogenous a uniform layer of PLLA. Bymeans of a surface profiler (Tenkor, AlfaStep 400) the average thicknessof the coating PLLA layer was determined to be 124±8 nm. (Group D)

A series (n=4) of PLLA-coated glass slides of group D was selected andadditionally coated by deposition of a skin layer on the top ofPLLA-coating. The polymer used for deposition of the skin layer was ablock copolymer poly(D,L-lactide-block-ethylene oxide)(PDLLA-b-MeO-PEO). The copolymer was obtained polymerization ofD,L-lactide in toluene using α-hydroxy, o-methoxy-poly(ethylene oxide)(MeO-PEO, MW=11000) as a macromolecular initiator withtin(II)-2-ethylhexanoate as a catalyst. The number average molecularweights of the PDLLA and MeO-PEO copolymer blocks were 17800 and 11000,respectively. The skin layer was deposited by spin casting a solution ofPDLLA-b-MeO-PEO copolymer in acetone (0.5 mg/ml) on the PLLA-coatedglass slides. Both sides of the slides were coated by the same procedureas for group D. (Group E).

Surface properties and interactivity of the polymer coatings in groups Athrough E were investigated by measurement of contact angles ofpolymer/water/air interfaces and by measurement of protein adsorption.

The dynamic contact angles, i.e advancing angle Θ_(A) and recedingcontact angle Θ_(R) of water on coated surfaces of glass slides weremeasured by Wilhelmi's plate Method using Kruss tensiometer. The valuesof contact angles reflect the wettability of the surfaces and areindirectly proportional to the interfacial energy or hydrophilicity ofthe surface.

The values of contact angles (degrees) of the polymercoating/water/airinterfaces for the series surface coated glass slides.

Series Θ_(A) Θ_(R) A (clean glass) 54.1 ± 1.2 40.9 ± 1.4 B (silaneactivated) 72.1 ± 3.4 59.7 ± 3.6 C (PLLA grafted) 82.1 ± 2.2 61.4 ± 2.4D (PLLA deposited) 81.5 ± 2.6 62.0 ± 2.8 E (PDLLA-MeO-PEO) 31.2 ± 1.632.4 ± 3.4

The values in the table demonstrate differences in surface energy(hydrophilicity) between the neat glass (series A) and glass slides withdifferent types of polymer coating. The values of contact angles forPLLA-grafted and PLLA-deposited layers are practically identical, thusindicating that a confluent layer of the same polymer material, i.e.PLLA, was created by both covalent grafting and casting from solution.By applying a layer of the amphiphilic block copolymer PDLLA-b-MeO-PEOas solution in acetone, which does not dissolve PLLA sublayer, ahydrophilic skin was created as the outermost layer of the coating. Themiscibility and, therefore, also good adhesion between the bindinggrafted polymer layer, the deposited PLLA layer simulating here apolymer container layer, and the polymer skin layer, was achieved byusing polymers with compatible structures, i.e polylactide in all threesublayers. The hydrophilicity of the skin layer is indicated by thelowest values of both advancing and receding contact angles.

The following additional observations have been made with the series Dand E. While the PLLA layers cast on a neat glass or a glass justmodified by the reaction with the silane reagent are unstable, i.e.,they peel off the glass typically within one or two days of theirincubation in the aqueous buffers, the PLLA layers of both series D andE, were stable and did not change contact angle values for more than 6days of the duration of this experiment. This observation demonstratesthe beneficial effect of covalently grafted binding polymer layer on thelong-term applicability of the coating.

The adsorption of serum albumin on the surfaces of series C, D and E wasfollowed by Comassie Blue staining, quantified by UV-VISspectrophotometer (Pye-Unicam 6200). The adsorption of the protein onthe glass slides with a hydrophilic skin coating made of PDLLA-b-MeO-PEOblock copolymer was at a level of 15 to 20 percent of that for PLLA(series D and C). Thus, hydrophilic skin on a polylactide coating canprovide for an antifouling properties of the surface and contribute tothe improved biocompatibility of the coated devices.

1. A method for coating a medical device comprising: (a) reacting thesurface of a medical device with a silane-based activating reagent toform a polymerized silane derivative covalently bonded to the surface ofthe medical device, said polymerized silane derivative containinghydroxyl or other functional groups that can be transformed intohydroxyl groups; (b) reacting the device of step (a) with at least onelactone monomer in the presence of a metal catalyst to form a lactonepolymer chain covalently bonded to the polymerized silane derivative,said chains grown on the hydroxyl or amino functional groups of thesilane derivative through in-situ ring opening graft polymerization oflactone monomers, said polymerization initiated by said hydroxyl oramino functional groups of the silane derivative covalently bonded tothe surface of the medical device, said lactone polymer chains and saidsilane derivative together forming a grafted lactone polymer layer; and(c) treating the device of step (b) with at least one polyester polymerlayer deposited on the grafted lactone polymer layer, wherein at leastthe first of the deposited polyester polymer layers is chemicallycompatible with the grafted lactone polymer layer to allow forentanglement of said deposited polyester polymer chains with the chainsof said grafted lactone polymer chains for strong adhesion, and whereinthe deposited polyester polymer layer is a lactone homopolymer or alactone copolymer.
 2. The method of claim 1 wherein the polyestercomponent of the deposited polymer comprises a lactone homopolymer or alactone copolymer, wherein the lactone homopolymer comprisespolyglycolide, poly(L-lactide), poly(D-lactide), poly(ε-caprolactone),poly(p-dioxanone), poly(dioxepanone), or poly(D,L-lactide), or whereinthe lactone copolymer comprises statistical or block copolymers, whereinthe statistical or block copolymers comprisepoly(L-lactide-co-D-lactide), poly(L-lactide-co-glycolide),poly(D-lactide-co-glycolide), poly(D,L-lactide-co-glycolide),poly(lactide-co-caprolactone), poly(lactide-co-dioxanone), orpoly(lactide-co-dioxepanone).
 3. The method of claim 2 wherein thelactone copolymer comprises a block copolymer wherein at least onepolylactone block comprises polyglycolide, poly(L-lactide),poly(D-lactide), poly(ε-caprolactone), poly(p-dioxanone),poly(dioxepanone), poly(D,L-lactide), poly(L-lactide-co-D-lactide),poly(L-lactide-co-glycolide), poly(D-lactide-co-glycolide),poly(D,L-lactide-co-glycolide), poly(lactide-co-caprolactone),poly(lactide-co-dioxanone), or poly(lactide-co-dioxepanone) and, whereinthe other block copolymer comprises polyalkyleneoxide, poly(amino acid),poly(acrylate), poly(methacrylate), or a polybutadiene.
 4. The method ofclaim 1 wherein step (c) is repeated two or more times to providemultiple layers of polyester polymer deposited on the covalently graftedlactone polymer layer.
 5. The method of claim 1 wherein the at least onedeposited polyester polymer layer comprises from about 0.5% to about 60%by weight of one or more biologically active agents.
 6. The method ofclaim 5 wherein the concentration of biologically active agent in thelayers of the coating may be the same for each layer or theconcentration may vary from layer to layer of the coating.